Continuity mistake: When Michael J Fox gets the elevator stuck the first time, one time there's a stain on the carpet, a repair man walks by and the stain is gone, he goes toward the elevator and the stain is back on the carpet.
Other mistake: When the executive team are jogging on top of the of sky rise, the last shot shows the building is in a horrible state of ruin. All the windows are broken out and it is definitely not the building Pemrose Corp was shown as throughout the movie.
Continuity mistake: In the scene in the empty office, as the camera angle changes, Fox's hair gets noticeably longer and darker.
Continuity mistake: When M.J. Fox enters the empty office and sits behind the desk, the phone rings, and he answers a grey phone. After a few cutaways, the phone has become black.
Continuity mistake: When Vera hands Brently a drink at the country house, and she's talking about how trees stuck up oxygen, you can see Michael slightly turn and dump the drink over his shoulder. When he turns back around the cup has stuff in it.