Continuity mistake: In a scene near the end of the movie, George enters the Building and Loan with a Christmas wreath on his arm. On hearing that he has a phone call from his brother Harry, he tosses the wreath on a table and picks up the phone. In the next second, the wreath is back on his arm.
Continuity mistake: When George Bailey crashes his car into the tree after leaving "Martini's Place", notice its position against the tree; an upward angle. In the ending scene when he's running home he cheers and taps the hood of the same car, now at a downward angle.
Continuity mistake: In a scene early on in the film, where George Bailey (James Stewart), Bert (Ward Bond) and Ernie (Frank Faylen) chat in the street, they suddenly stop due to the appearance of Violet (Gloria Grahame) in her "this is what I wear when I don't care how I look" dress. The camera cuts back to them and we see a dark haired woman in a hat pass in front of Ernie's taxi. As Violet crosses the street and gets honked at, we see another shot of the boys staring after her - and the dark haired woman passes in front of the taxi again.
Continuity mistake: In the confrontation scene between Peter Bailey and Old Man Potter, Peter moves from behind his desk about four feet away from Potter, to sitting on the edge of the desk about 18 inches away from Potter. Also the coat on the coat rack behind Potter changes from hanging from the collar loop to just the collar itself.
Continuity mistake: In the scene at the railway station where George and Uncle Billy are waiting for Harry, Billy reaches in the bag of peanuts and pulls one out. As the camera angle changes slightly, Billy's hand is suddenly back in the bag and pulls out another peanut. Also the man in the background wearing coveralls and a locomotive cap changes his position, and has lost the pamphlet he had just placed in his back pocket.
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: 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.
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.
Continuity mistake: When George Bailey is going to jump off the bridge, watch the snow carefully. In one of the shots where Clarence is shouting in the water the snow all of a sudden quits, then it goes back to snowing when George jumps in.
Continuity mistake: When Uncle Billy sees Potter in the bank, he walks to the teller window and there's no line, but a second later there's a line of a dozen or more people behind him.
Continuity mistake: When George is kicking stuff and knocking stuff over in his house (after yelling at his children), his hair is messed up. In the next shot, it's combed again.
Continuity mistake: During a confrontation between old man Potter and Peter Bailey at the Building and Loan, Potter's bodyguard stands behind the wheelchair on its left side. But in the close-up shot of Potter, the arms and hands of his bodyguard can be seen extending from the right side of the wheelchair. In the next full screen shot, the bodyguard is seen on the left side of the wheelchair once again.
Other mistake: In the scene on the bridge, before Clarence jumps, George's hands do not indent the 2-3" of snow on the rail. In a later shot, after George jumps, you see two snow-less spots on the railing.
Visible crew/equipment: When Mary leans across the drugstore counter to whisper in George's bad ear, there is a small piece of tape on the edge of the counter right in front of her hand, presumably to show the actors where to position themselves for the shot (the tape isn't visible in the other shots showing that same section of the counter).