The only family member absent from the film is Dana, who according to the script is off at university, but a scene explaining away her absence was never filmed. Dominique Dunne was murdered by her boyfriend John Thomas Sweeney (who later changed his name to John Maura and disappeared) shortly after "Poltergeist - Demoniache presenze (1982)" premiered. Ultimately, no mention is made of Dana in the final film, or of her being in college. It was decided by the filmmakers to retire the character and not recast her out of respect for the deceased actress and her family.
Heather O'Rourke was so afraid of Julian Beck (Reverend Kane) the first time she saw him that she burst into tears.
Julian Beck's gaunt appearance is the result of the stomach cancer that would claim his life. This is his final film appearance.
The film had an original running time of 131 minutes before being edited down to 91 minutes. Some have surmised that MGM rushed production and ordered the cuts, e.g the final battle with Kane lasts all of two minutes. Zelda Rubinstein in particular was furious about this, as she felt her best scenes were removed from the final cut.
H.R. Giger provided the special effects designs. Giger created several designs but only two made it into the film, albeit briefly. Some books on his art report that Giger was "very unhappy" with how his designs were translated to the film.