Continuity mistake: When Benjamin is running up the stairs of his rooming house with a stack of presents and a big bouquet of flowers, the flowers are pointing down held by his left hand with the presents in front of him. When he rounds the corner of the stairs, the flowers are upright in front of both him and the presents.
Factual error: There is a scene with Benjamin Braddock going to Berkeley, but his car is driving on the upper deck of Bay Bridge which only goes in the direction of San Francisco.
Continuity mistake: Benjamin says to Mrs. Robinson, "I'm going home now, I apologize for what I said" as he walks out of Elaine's room. In the next shot as Mrs. Robinson walks out, if you look very closely everything on the three shelves to the left and right of Elaine's picture has been rearranged.
Continuity mistake: Mrs. Robinson sits at the bar and asks Benjamin, "Did you know I was an alcoholic?" and the silver shaker bottle with the large ring on top of it moves from the back of the bar to being between Mrs. Robinson and the radio she turns on, on the left wall. A few shots later it moves back again.
Continuity mistake: Benjamin breaks into the Robinson's house and runs upstairs looking for Elaine but finds Mrs. Robinson instead. As she picks up the phone to call the police we see nothing on the bed except a blue pillow. In the next shot there's a lot of other things now covering the blue pillow.
Plot hole: In one scene, he's driving from Los Angeles to Berkeley in a hurry, and crosses the bridge again (in the wrong direction). But the most direct route from L.A. to Berkeley doesn't require you to cross the Bay Bridge in EITHER direction.
Continuity mistake: When Benjamin is in his apartment, there is a Coors can on top of the refrigerator. When the camera comes back to the refrigerator, the can is gone.