Horror House was selected by Quentin Tarantino for the First Quentin Tarantino Film Fest in Austin, Texas, 1996. The film was drastically re-written, re-shot, and re-cut by writer/director Gerry Levy (under the name Peter Marcus) at the insistence of one of the US producers. Original writer/director Michael Armstrong's commentary on at least one version of the DVD goes into this in detail. Relatively little of the material outside the house was originally in the film and much of what remains was used differently. None of the material featuring George Sewell was shot by Armstrong and only one scene with Dennis Price (in the nightclub) was his. The motivation of the killer was changed and the relationships between the young people were considerably softened. Michael Armstrong's original script was much more psychedelic and envisaged David Bowie in the role of Richard, but he was overruled by AIP, as it was considered that Bowie would clash with Frankie Avalon. He was replaced by Noel Janus, but objections by Equity led to him being replaced with Julian Barnes (who had originally been cast as Henry). 

Leading lady Jill Haworth was on drugs during filming. Boris Karloff was offered the role of the Police Inspector but health problems forced him to decline. He was instead offered a smaller role as the film's narrator but this was scrapped when his health deteriorated further. The theme music by The Pretty Things/ Electric Banana would be used for the 1971 BBC thriller, The Passenger. Carol Dilworth would later marry Tremeloes singer/bassist Len 'Chip' Hawkes and have a child, Chesney Hawkes, together.