Continuity mistake: When Carol enters Melvin's building soaking wet to tell him she'll never sleep with him, we can see bra straps across her back under her blouse. But at Melvin's door, she's embarrassed to discover that the wet blouse reveals a distinct lack of a brassiere.
Visible crew/equipment: Early in the movie, Melvin walks for the first time to the restaurant in which Carol works. As Melvin turns the corner on the sidewalk and walks towards the camera, he is surrounded by extras playing people he must dodge. If you look in the center and right background, you will see New York spectators standing in the middle of the street, watching the movie being made. (00:10:20)
Continuity mistake: When Melvin and Carol enter the restaurant on their trip, a certain song is playing (I can't recall the song). Melvin leaves to buy a jacket, returns, and just after they are seated, you hear the female band leader say, "Here's a special song for...", and it's the same song they played 10 minutes ago. (01:34:00 - 01:38:15)
Revealing mistake: Midway through the film, Carol is on a bus heading to Melvin's apartment in Manhattan. She is going to tell him that she won't sleep with him after he has given her son free medical care. She is in a pensive mood and the camera pulls out showing her in the window. As the camera pulls out further, the readable sign on the side of the bus says "not in service." (01:02:55)
Continuity mistake: Simon's cut on his lip is quite visible in the car on the trip down to Baltimore and on the way back to New York, but it miraculously disappears while they are staying in the hotel in Baltimore.
Continuity mistake: In the restaurant scene with Melvin and Carol, when she is taking her drink from the bar to their table with the help of a waiter, when she first picks up her drink there is very little in it, but when she takes the drink from the waiter and places it on the table it is practically full. (01:33:25)
Continuity mistake: Before Carol takes a bath she tries to help Simon out of his shirt. In spite of being handicapped by his cast he insists on doing it by himself, although with difficulties, but he would never have managed to get out of his black pants into his jammie shorts between shots. (01:41:40)
Continuity mistake: After Simon has to dismiss his housekeeper, she is leaving the apartment with her large purse in one hand and several carrier bags in the other. She then lifts her hand, which is now empty, and says, "But who's going to walk Verdell?" There was no time for her to shift or drop her purse.