When Robert Zemeckis was trying to sell the idea of this film, one of the companies he approached was Disney, who turned it down because they thought that the story of a mother falling in love with her son (albeit by a twist of time travel) was too risqué for a film under their banner. In fact, Disney was the only company to think that the film was risqué. Every other company said that the film was not risqué enough, compared to the other teen comedies at the time (Fast Times at Ridgemont High, Revenge of the Nerds, Porky’s etc).
(Source: filmtrivia)
