Factual error: In the closing scene Ernie the cab driver is wearing a military shirt with an Air Force insignia on the sleeve, but we were told earlier that Ernie parachuted into France. His shirt should have had a different patch.
Continuity mistake: The old man's cigar disappears when he sends young George to deliver a prescription.
Other mistake: During Harry's party, when George is outside talking to his mother she encourages him to see Mary and George says "Point me in the right direction." He then exits right and immediately returns. As he passes by, there is a glitch in the film and for a brief moment everything speeds up. This is most evident if you watch the people dancing in the house because they appear as though they clicked into "fast-forward motion" briefly and then return to normal.
Continuity mistake: In the scene where Old Man Potter is offering George a job, nearly all of the items on Potter's desk - skull, lighter, eye glasses, small ink blotter and magnifying glass - change position as POV shots change from Potter to George. In some cases items disappear completely then reappear, ie. eyeglasses, ink pot and two pens, the liquor case and bells on the corner of the desk, and the pencils beside Potter go from none to one to two, and then none again. (01:07:30 - 01:12:40)
Continuity mistake: Potter's rent collector is showing Potter a map of the new houses George Bailey built, but a page is folded over on the desk, covering half of an ink pen set on the desk. When the rent collector prepares to leave, that page is now a few inches to the right of the ink pen set (viewer's perspective) and hanging off Potter's desk entirely.
Audio problem: When George is talking to Harry on the phone regarding being decorated with a medal of honor, he is at his office. The guy to the right of him starts to say "what is he saying?" but the audio cuts off just before he finishes "saying." The scene cuts to a closer shot of George talking, so why did the audio cut off?
Continuity mistake: When Ernie is about to take George during his "never born" sequence, if you look at the building next to the taxi, there is the Indian Club. As Ernie is driving along around 20-30 seconds pass inside the cab. When we see outside the cab and Ernie signals to the policeman, you can see the cab has only traveled roughly 20 meters from the Indian Club.
Factual error: When Clarence picks up his copy of "Tom Sawyer" to see if it is dry, the book is in perfect condition, despite their clothes being soaked. The pages of book that had been soaked in water would been swollen and wrinkled, and many pages would very likely have stuck together as the book dried.
Continuity mistake: In the scene where Violet and George talk about going up to Mount Bedford, they start their walk down the promenade, close to the intersection where Gowers Drugs and The Bijou theater are visible in the background, along with a tree with no visible branches and a Caucasian couple seated on a park bench facing screen right. At the cut to the closeup, they have moved about 50 to 75 feet further down the promenade, the drug store and theater are no longer visible, the tree behind them now has a branch, the couple is now African American and the park bench is facing screen left. (00:41:30)