There is a DJ known as Nocturnal Ned who works at Arnold's hometown radio station MJZZ. Nocturnal Ned is actually a caricature of "Hey, Arnold!" creator Craig Bartlett, who also provides his voice in various episodes.
In episode "World Records", one of the records in Arnold's book is set by a fictional person named Frannie Caudell. The voice of Helga is Francesca Smith, and the voice of Arnold at the time was Toran Caudell.
Sid has been voiced by two brothers: Sam Gifaldi for most of the series, and one time by Taylor Gifaldi.
The show began as a series of claymation shorts by Craig Bartlett, many of which aired on "Sesame Street" (1969).
The girls of the show are based on girls that creator Craig Bartlett liked as a kid.
The city that Arnold lives in is a combination of Seattle, Brooklyn, and Portland. There are possible hints that the city is called Hillwood. For example, the Hillwood Medical Center or Hillwood Zoo.
The character of Mr. Green the butcher is based on Ernest Borgnine's character in the 1955 film, Marty (1955).
Throughout the series, Arnold's last name is never mentioned.
The name of the boarding house is Sunset Arms Boarding Home.
The sign outside the Sunset Arms Boarding House reads "No Children, Pets OK". This sign can be seen in various places in other episodes, most noticeably at the pool Arnold and Gerald unsuccessfully get into in the heat wave episode.
Ruth P. McDougal was originally Arnold's love interest, and as Arnold talks about her, Gerald constantly tells him that it's hopeless because she's a sixth-grader. However, as Lila was introduced, Ruth was phased out.
This series was originally supposed to end with three half-hour episodes. These episodes became Hey Arnold! The Movie (2002).
Oskar Kokoschka's name is taken directly from a turn of the 20th century Viennese painter, though their personalities are completely opposite.
In the Halloween episode where Arnold and his friends fake an alien invasion, the name of the place where the "U.F.O." (actually the water tower with Christmas lights) landed is Well's Ridge. This is a reference to Orson Welles, who did a fake radio broadcast in which aliens landed on Earth.
The Halloween episode is an almost portrayal of Orson Welles's The War of the Worlds (1953) radio broadcast in 1938.
The character Eugene Horowitz gets his name from Michael Landon's birth name, Eugene Orowitz.
Arnold's grandfather drives a Packard.
Many stores in the city are named after the writer's and director's in the city - such as Viksten's Pharmacy and many others.
What actually happened to Arnold's Parents was never revealed
When Stinky starts recording TV commercials, the studio has a gate that reads "Snee-Oosh Studios." This is the actual name of the studio that worked on the show.
This was the first animated series on Nickelodeon to use children as voice actors.
[Grandpa believes he has died]
Grandpa:
Well, that's it. I must be in heaven. Oh, no! Oskar's here! This must be the other place!
Harold Berman:
Wow, you really are crazy. Wanna join our club?
Helga:
I am too a girl. I'm pretty. I'm feminine. I'm delicate.
[Helga bumps into someone]
Man:
Oh, excuse me young man.
Helga:
I'm a girl!
Nick Vermicelli:
This time I'll be a 50% partner.
'Big' Bob Pataki:
20.
Nick Vermicelli:
40.
'Big' Bob Pataki:
20.
Nick Vermicelli:
30.
'Big' Bob Pataki:
20.
Nick Vermicelli:
Deal.
Miriam Pataki:
I have to go work. Somewhere.
[Harold gets hit with a baseball]
Harold Berman:
Easy squeezy lemon peasy.
Grandpa:
Sounds like young Arnold's got another one of his complex labyrinthine conundrums of a boyhood problem.
[Arnold steps up to bat]
Arnold:
Wind's in the east. I should probably shoot for the gap between second and third.
Gerald:
Just try not to get hit, okay?
Arnold:
Yeah, good strategy.
Helga:
Come on, come on.
Harold:
Alright already. Keep your shirt on, Helga, for all our sakes.
Arnold:
Hey Grandpa, I've got a problem.
Grandpa:
Shoot it at me, short man.
Arnold:
Well, see, there's this big jerk at school, he says he's gonna...
Grandpa:
- says he's gonna beat you up, eh?
Arnold:
Well, yeah.
Grandpa:
Gonna give you 24 hours to dangle, eh?
Arnold:
That's right!
Grandpa:
Big guy, huh? Slow, but with lots of power. Squash you like a bug, eh?
Arnold:
Yeah, yeah! What should I do?
Grandpa:
I have no idea.
Arnold:
I've got to think of something, Grandpa.
Grandpa:
Well, you could skip town. But then you'd have to live the rest of your life in fear, always looking over your shoulder, waiting for... that day. You try reasoning with him? Oh, a moron, eh? Well Arnold, I wish I knew what to tell you. In eighty years I think I've only learned one thing for sure.
Arnold:
What's that?
Grandpa:
Never eat raspberries.
[Grandpa holds his stomach]
Grandpa:
Gotta go!
[Grandpa runs to the bathroom]
DJ Nocturnal Ned:
It's 7:00 on KILL. This one goes out to Arnold, who's going to die in 2 hours, 6 minutes, and 47 seconds, from Helga who hates you.
[the kids are thinking of ideas for something to do]
Curly:
I say we paint ourselves with tiger stripes, and go free all the animals in the zoo!
Helga:
[sarcastically] Fine, Curly. We'll meet you there in an hour.
Curly:
[runs away cackling]
Helga:
Poor twisted little freak.
Gerald:
Wanna go throw rocks at Helga throwing rocks at a dumpster?
Arnold:
Sure.
Arnold:
It's not insurmountable.
Gerald:
Insurmountable? Man, you read too much.
Mr. Hyunh:
How big was this punk?
Arnold:
Big.
Mr. Hyunh:
Big punk?
Grandpa:
Oh, simmer down, you hot-headed loony!
Arnold:
Brainy? What are you doing here?
Brainy:
Um.
[wheeze]
Brainy:
Something.
Grandpa:
Everything in nature is beautiful. Unless it's ugly.
Arnold:
What's scat?
Grandpa:
You know, scat. Droppings. Like what you're standing in.
Big Bob Pataki:
Remember, we'll beat any advertised price. Unless it's lower.
[after Grandpa Phil gave him advice]
Arnold:
Thanks, Grandpa.
Grandpa Phil:
Sure, Arnold, anytime... Except next Wednesday at 3:30. I'm having a wart removed then.
Helga:
Move it, football head!
[as they are about go into the Tunnel of Love]
Harold:
I don't want to go into the Tunnel of Love with you Rhonda!
Rhonda:
Oh I know you like me Harold!
[as she grabs him in the ride and as they head off into the Tunnel of Love]
Harold:
NO I DON'T! HELP! HELP!
[as Harold and Rhonda are assigned to partner up taking care of an "egg baby"]
Harold:
Oh, come on, Rhonda, I know you like me!
Rhonda:
[nervously] What makes you think that?
Harold:
Remember that time at the Cheese Festival...
Rhonda:
[claps a hand over Harold's mouth] I thought I told you never to mention that night again.
[as Arnold & Eugene Horowitz are going in a Roller Coaster]
Sid:
He's a goner...
Gerald:
He's a brave boy...
Harold:
He's a saint he gave me his tokens...
[Censored Line as he is about to be denied entry of the Tunnel of Love]
Sid:
What, because I'm short means I can't get no action!
[about riding the subway]
Gerald:
Sun goes down, stay above ground.
Grandpa:
[Grandpa is reading out of Arnold's father's journal, an entry describing a volcanic eruption] "It was terrifying and beautiful all at the same time"
[to Grandma]
Grandpa:
kind of like you, Pookie.
Helga:
There is no way I'm taking the subway.
[next frame]
Helga:
I can't believe I'm taking the subway.
Helga:
[after weasling out of paying a dinner bill] There is no way I'm gonna go back in there, tell them the truth, and wind up washing dishes.
[next frame]
Helga:
I can't believe I told them the truth, and I wound up washing dishes.
Gerald:
[about the last boat available for a fishing contest] There is no way we're fishing in a swan boat.
[next frame]
Gerald:
I can't believe we're fishing in a swan boat.
Arnold:
There is no way we're calling our go-cart the Mauve Avenger.
[next frame]
Arnold:
I can't believe we called our go-cart the Mauve Avenger.
Oskar Kokosha:
[about to bet Arnold's CD player during a poker game] Don't worry, Arnold, there's no way I can lose.
[next frame]
Oskar Kokosha:
I can't believe I lost.
Phoebe:
Well, I suppose the only solution would be to tell the manager the truth.
[pause]
Helga:
That is the stupidest idea I have ever heard in my entire life!
Sid:
[to Curly, dressed as a dead bride] I can't believe you'd pull such a dirty trick!
Eugene Horowitz:
I can't believe how nice you look in that dress!
Oskar Kokosha:
You keep the money.
Mr Hyunh:
This lint is your lint.
[in high pitch voice]
Mr Hyunh:
I'm not your Mother!
[on a camping trip, Grandpa is showing Arnold and Gerald survival skills. Gerald is eating red berries. Arnold is eating green berries]
Grandpa:
Now, only do this under adult supervision. Red and sweet are good to eat, but I swear by this sonnet, green will make you vomit.
Arnold:
[swallows] I thought it was green and sweet are good to eat.
Grandpa:
No, I've been saying it all morning. Red and sweet. Red and sweet.
Arnold:
Excuse me a minute.
[Arnold runs off screen and vomits]
Grandpa:
[sarcastically] You're vomiting, aren't you, Arnold?
[Helga is doing stand-up in the school juice bar]
Helga:
My first impression is someone we all know. It's the first voice you hear in the morning, and it goes something like this:
[imitating Principal Wartz]
Helga:
"Attention, students of P.S. 118, I have an important announcement. Henceforth, all lunch-related activities shall be conducted during the lunchtime period."
[normal voice]
Helga:
Whoo, thanks for clearing *that* up, Principal Wartz.
Continuity: In "Phoebe Cheats", she wakes up and talks to the statue trophy she illegitimately won, and repeatedly changes from a blue sweater to a night grown and back again between shots.
Continuity: In "Girl Trouble", Helga manages to be both in her seat and standing at the front of the class sharpening her pencil. At the same time, all the desks appear to be arranged in rows, but when she talks to Arnold seconds later, they are in groups.
Continuity: In "Jamie O. in Love" the license plate on the front of his car reads "KILLER", while the back reads "KILLR".
Continuity: In "The List", Grampa Phil pours five pieces of cereal into a bowl, but in the next shot there are only three.
Continuity: In "New Teacher", all the students' positions switch around between shots as Principal Wartz announces about the old teacher retiring in the beginning of the episode.
Continuity: In "Miss Perfect", while the girls are talking how Lila is a little Miss Perfect, Rhonda's clothing alternates between the new clothes she brought to school and "everyday" wear.
Audio/visual unsynchronized: In "Harold's Kitty", we hear Harold's mother pound on his bedroom door to warn about cat messes, yet in the same shot (and in subsequent shots) the door is wide open.
Continuity: In "Harold's Kitty", when the neighborhood tries to persuade Harold to give up the cat, his parents jump from the sidewalk to in front of the door and back again between shots.
Plot holes: In "24 Hours to Live", Helga calls and says "22 hours and 46 minutes until you die,". He then talks to Grandpa and goes up the stairs and talks to Grandma. The phone rings saying Arnold has 22 hours and 14 minutes. This means that it took half an hour to walk up the stairs.
Plot holes: In "Biosquare", Arnold and Helga enter the greenhouse at 8:00 AM and must stay in there for 24 hours. When they wake up the next morning, Arnold claims there is six hours to go. This means it is 2:00 AM yet the sun is up and shining.
Continuity: In "Student Teacher", before Olga is about to board the plane, her luggage disappears for a brief moment.
Follows
Arnold Rides His Chair (1991) (TV)
Followed by
Hey Arnold! The Movie (2002)
Spin off from
Arnold Escapes from Church (1988)
The Arnold Waltz (1990)
Hey Arnold!: 24 Hours to Live (1996)
Referenced in
Road Trip (2000)
Jimmy Neutron: Boy Genius (2001)
Undercover Brother (2002)
Finding Nemo (2003)