Rosemary's Baby is perhaps the single most faithful adaptation of a book to film ever created – with a script that's less an adaptation than a near-literal transcription of Levin's novel, carrying over its most minute details: its 'slow-burn' tension-building, its ratcheting paranoia, its scene structure, dialogue, descriptions, its dark wit, its is-it-real-or-is-it-imagined ambiguity.

  “Polanski showed me how he was going over the book the other day,” Mr. Levin told PW, in the tone of an author who can hardly believe his good fortune. “He doesn’t want to change a thing! All he was doing was cutting out descriptive passages.”
    —Publisher's Weekly (1967)

In fact, you'd be hard-pressed to find any material elements in the film that aren't direct transfers from the book:

Even many of the movie's signature visuals hail from the book: Minnie Castevet through the peephole... Guy and Roman seated just out of view... the entire six-minute 'dream' sequence... They're all stroke-for-stroke renderings of the novel's descriptions. Even much of the costuming comes straight from the book. (Ditto the Vidal Sassoon haircut.)

  “Having read Levin’s book, I can tell you that reading each line of every page is exactly like watching the story unfold on screen. It is the most faithful adaptation I’ve ever read, more like reading the script after the fact.”
      —TheLastDriveIn.com (2011)

(Left to right) Levin with Mia Farrow and John Cassavetes on location at The Dakota

 
That's no slight to the film – its direction, performances, cinematography, production design, and brilliant Krzysztof Komeda score combine with its very unflinching fidelity to Levin's novel to create a classic that now deservedly resides in the National Film Registry.

So it comes as no surprise that Levin found Rosemary's Baby to be the most successful film adaptation of any of his works, by a wide margin. Living at the time of its release in Connecticut, he told the Westport Town Crier's Barbara Plunkett “I couldn't ask for a more faithful job,” though Plunkett herself found the film to be “lacking some of the high suspense and fright of the novel.”

Indeed, as faithful as the film is, it still omits significant additional layers present in the book.

“Despite Polanski’s incredibly faithful approach to bringing [Rosemary's Baby] to life on the big screen, the film lacks the depth of Rosemary’s interiority that Levin’s novel provides.”
    —Collider, 2023

LEVIN-ON-LEVIN

  “I’ve never done any of the screenplays of my work, although invariably I’ve felt I should have done. The only one I was actually involved in was Rosemary’s Baby. That was the most satisfying film of my work. Roman Polanski kept ringing me to ask my advice when he was writing the script and it contains scenes and dialogue that are completely unchanged from the novel.”
    —Levin (London Evening Standard, 1994)

  “I saw a big, loud Midwestern woman when I wrote Minnie Castevet, but the casting of Ruth Gordon, who was quite small, didn’t bother me, because she was big in other ways. However, I’ve always thought John Cassavetes was miscast [as Guy], because you always knew he was up to no good. Cassavetes was just that kind of actor – intelligent, talented, attractive even, but so saturnine. I felt Guy should have been [played by] Robert Redford. He would have been ideal. His handsomeness would have given him the perfect cover, because he looks incapable of evil. That kind of Guy would have made [the character of] Rosemary more believable, although Mia had such radiant innocence you believed that she would trust even John Cassavetes!”
    —Levin (Opera News, 1997)

SUGGESTED READING/VIEWING
• Book-to-Film Comparison (IraLevin.org)
• Our gallery of photos of Levin on location at the Dakota

FUN FACT
• According to the New York Post of September 30, 1967 – the Dakota's exterior was rented out for $1,000 a day — with one of the co-op's owners stating "The only kick is we didn't make more. It came to $4,000 or $5,000."

OTHER ADAPTATIONS
• "Look What's Happened to Rosemary's Baby" (1976)
• "Rosemary's Baby" (Mini-Series) (2014)