Continuity: Across Series 3 - 5, Ross remains the same age (29) for all three years. In Series 3 he tells Chandler, "No thanks, I'm 29" when offered chocolate milk; in Series 4 when the guys try to party without Gandalf they all say they're 29; and in Series 5 when he's trying to reconcile with Emily, he says either he does, or he would get divorced for the second time before age 30.

Deliberate "mistake": The show is set in New York. Joey was a cast member on Days of Our Lives, which is filmed in Los Angeles, but is still always around.

Continuity: In S1 E1 a lady is seen walking past the window of Central Perk. In series 10 the same clip is used - everything's identical despite 10 years passing.

Factual error: Phoebe's greatest love David leaves her to go to Minsk and comes and goes throughout the whole show, telling stories of Minsk on the way i.e. of the long months when the sun does not rise and the constant freezing cold. Minsk, being the capital of Belarus (although claimed to be in Russia for reasons explained in Corrections), is approximately as high up north as i.e. Wales and northern coast of Germany, and even during the winter months there is always daylight for several hours. Although winters in Eastern Europe are cold, the kind of coldness described by David would more believably happen in Siberia than Minsk, and the summers are just as nice and hot as everywhere in Europe.

Deliberate "mistake": The only time that any apartment doors are locked is when it is important to the episode. For example, Monica's apartment door is always unlocked, even when they go out or she and Chandler are having sex, but in "The One Where Underdog Gets Away" (Series 1), it's locked when there is all the "got the keys?" business. Also, Ross' apartment is never locked, except for in "The One With Phoebe's Birthday Dinner" (series 9), when they lock Emma in, and in "The One With The Engagement Picture" (S7 E4) when Phoebe has the key and unlocks the door then Ross demands it back.

Continuity: Across the whole show, the infamous wall in Rachel's room / guest room (Monica's apartment) changes. When the room is not being filmed, the wall is as normal, but on quite a few episodes, when the room is actually used for scenes, the wall is much shorter. In both the episode where Ross buys Phoebe a bike, and where Phoebe and Rachel have to live with Monica after their apartment caught on fire, people are able to walk straight into the room without the wall being in the way.

Audio problem: Any scenes outside Central Perk always sound as if they're on a set (which let's be honest, they are) - the sound is often muted and footsteps on the pavement have a very slight echo to them.

Continuity: The view from Monica's apartment changes after the first few episodes.

Continuity: Joey is shown moving into Chandler's apartment and meeting everyone for the first time approximately one year before Rachel showed up. It is also mentioned that it is a warm time of year, indicating that it is set during the summer months. However in 'The One with All the Thanksgivings' (series 6) Joey is shown living with the Friends by Thanksgiving (i.e. November) 1992.

Factual error: Chandler and Monica's wedding day is May 15th, as mentioned on the show. In Series 9, some time in January (as it is after the characters have celebrated Christmas and New Year), it is established that Rachel has been on maternity leave for five months, which means she took her leave in August. Since she realised she was pregnant in May the year before, this means her pregnancy lasted from April/May 2000 to August/September 2001, a time span of 16 to 17 months. This cannot be explained by saying that episodes don't have to take place in the month they air, as we are given the dates by the characters on the show.

Continuity: The Chick changes breeds and gender a couple of times. It starts out as a full size White Leghorn. During the adolescent phase it is a female White Silkie. This is a bantam or small size chicken. In maturity it is a male White Leghorn.

Continuity: The arrangement of Joey and Chandler's bathroom changes. In 'TOW the boobies', the shower is opposite the door, but in other episodes, the sink is opposite the door.

Continuity: The number of the flats near the start of the first series was 4 and 5. After a few shows they changed to 19 and 20. [The producers realised that the numbers 4 and 5 were for apartments on the lower floors and had shown Monica's apartment to be much higher up so they changed the numbers - it's still a mistake but there's the reason.]

Continuity: In the pilot episode, the guy Rachel left at the altar is called Barry Finkel. In all the other episodes his name is Barry Farber.

Continuity: Mr Heckles's apartment number changes from 8 to 5.

Continuity: The door to Monica's bedroom is shown open, then closed, then open, and then closed during the scene in which Paul arrives for their date.

Continuity: At the end of the episode when Ross picks up his jacket, there is a blue bowl on the small table by the pillar and nothing on the main kitchen table. In the next shot, the blue bowl has moved to the large table.

Continuity: In the scene where the friends scoot the table over to see Monica's date with "Paul the wine guy", the cup in front of Chandler changes position.

Continuity: When Ross, Chandler and Joey are setting up Ross' furniture and Ross is bent down saying, "And I cannot feel my legs," Ross is holding a manual. When it cuts, the manual is on the floor.

Continuity: When Monica is saying bye to Paul, Paul goes to the screen left but the stairs are at the screen right.