James Spader was offered the role of Blane, but he chose to take the role of Steff instead. He finds it more fun to play the villain.
The filmmakers wanted Blane, to be "a hunky, square-jawed jock," but Molly Ringwald wasn't attracted to that sort of guy. Ringwald had some say in the casting, and after Andrew McCarthy auditioned, she told John Hughes and Howard Deutch her thoughts on him. "That's the kind of guy I would fall in love with." They thought he was a "twerpy guy", and weren't interested, but Ringwald pushed for his casting.
The genesis of this project emerged when Molly Ringwald asked John Hughes to write a movie based on The Psychedelic Furs song "Pretty in Pink", which was her favorite song at the time.
When the ending was re-shot, all of the principal cast members had to be called back. Andrew McCarthy had already lost a substantial amount of weight and shaved his head for a new role in a New York City play called "The Boys of Winter". Although he wore an auburn wig, he's noticeably more gaunt in the re-shot scenes.