Continuity mistake: Near the end of the movie, when George Peppard is talking to Audrey Hepburn in the alley and it's raining heavily, his hair switches between being combed back and combed to the side. Very obvious - this takes place several times.
Revealing mistake: In the taxi scene at the end of the movie, the steering wheel turns back and forth but the driver's hands are not moving.
Continuity mistake: When Holly and Paul are at the library viewing Paul's book, Holly encourages Paul to autograph the library's copy of his book. Paul grabs a pen off the library's counter and begins to write in the book, then in the next shot Paul once again takes the pen from the library counter to write in his book.
Visible crew/equipment: Just before Paul sits down on the box in front of Holly to show her the book commission that he had just earned, a microphone flashes into view on the right side of the screen.
Continuity mistake: When Holly gets out of the taxi into the pouring rain to run after Paul, she is soaking wet before her feet hit the sidewalk.
Continuity mistake: In the bedroom scene where "Fred", (Paul Varjak) is talking to Holly the wrist watch he is wearing disappears and then reappears.