According to the DVD special features, Crispin Glover auditioned for the role of Marty McFly before being cast as George (Marty's father).

Jeff Goldblum was considered for the lead role of Doc Brown.

Melora Hardin (from TV's The Office) was cast as Jennifer Parker, but was replaced when Eric Stoltz was fired and replaced with Michael J. Fox. She was considered to be too tall to be Marty McFly's girlfriend.

C Thomas Howell was considered for the lead role of Marty McFly.

Lithgow was consdiered for the role of Doc Brown.

Ralph Macchio reportedly turned down the part of Marty McFly.

Eric Stoltz was actually hired to play Marty McFly in Back to the Future, and was replaced later with Michael J Fox.