"Handling of the script... plays the horror tale fairly straight so what's happening is not too illogical until the finale wrapup, when all restraint comes off and the melodramatics run amok. ...Basil Rathbone is quite credible as the surgeon, enough so that the brain operations he performs will horrify many viewers."
Variety.

"Seldom, if ever has the X certificate been so richly earned. ...The cast, which includes many specialists in Grand Guignol, really gets to work on the grisly malarkey and, except for an unintentional near slapstick climax, invests it with plausibility."
Kinematograph Weekly (Britain).

"Rathbone has a grand time as the mad scientist, assisted nobly by some of the best names in the horror field. Audiences should be frightened plenty, and past experience proves that this can mean good grosses... Sure, a lot of it is corny, but it is all good fun in a grisly, frightening manner."
Motion Picture Exhibitor.

"Never before (or since) have so many horror actors been brought together and told to act like mongoloids. Never have so many actors been so wasted. Only Basil Rathbone and Akim Tamiroff get to play semirational humans."
Michael Weldon, The Psychotronic Encyclopedia of Film.

"Rathbone is splendid throughout. It's a typical role for him but, thorough professional that he was, he rises to the occasion. He even does something I didn't think was possible; in one brief, wordless scene, he indicates the depth of Cadman's passion for his sleeping wife, and the look on Rathbone's face and the slight gesture he makes will literally be with me the rest of my life. As he sees the deformed victims advancing on him, Rathbone sighs very slightly, and for a moment rests his cheek on that of his beautiful wife. In his eyes is a look of sad resignation, which may have been his attitude toward the film. But it's fine and touching, and almost validates The Black Sleep.
Bill Warren, Keep Watching the Skies: American Science Fiction Movies of the Fifties.

"Budgeted at approximately two hundred-fifty thousand dollars, the production's strongest asset was its cast, which included three performers (Chaney, Carradine, and Bela Lugosi) closely associated with the horror genre. Their talents were sadly wasted, as no overall mood of terror or suspense was created in the film."
Michael B. Druxman, Basil Rathbone: His Life and His Films.

"The film ought to be required viewing for Hammerheads who like to boast that that company's The Curse of Frankenstein (1957) was the first film to break a number of 'taboos' that were actually already broken by The Black Sleep. The sounds of stabbing and sawing are heard as Basil Rathbone cuts open the sailor's scalp; close-up shots of his exposed fluid-seeping brain are seen; there's also some strong on-camera violence, including a close-up of Phyllis Stanley's screaming face as she's held down in the blazing fireplace. ...Among the 'horror stars,' all acting honors go to Rathbone, who gives a fine performance as Cadman. Peter Cushing has the reputation of inaugurating the character of the tilted, elegant, silver-tongued but single-minded monster maker, but Rathbone did it first and did it much better..."
Tom Weaver, Midnight Marquee Actors Series: Bela Lugosi.

"Film lacks acting character but has plenty of character acting. ...Film is in dire need of atmosphere – you would be wise to give it the air."
John Stanley, Creature Features Movie Guide.

"Only Tamiroff gives a decent performance, and his work is all that gives Sleep any real worth. Certainly the by-the-numbers direction and the dreadful script don't help matters, nor does the obviously cheap production. Diehard horror aficionados may enjoy The Black Sleep, but most others will be disappointed and then irritated by it."
Craig Butler, All Movie Guide.

"Le Borg's direction is pedestrian and the script by Higgins (best known for his series of hard-edged thrillers for Anthony Mann in the forties) is surprisingly plodding. Rathbone gives an evocative performance, as does Lugosi who is silent throughout."
Phil Hardy, The Encyclopedia of Science Fiction Movies.

"Big horror cast cannot save dull, unatmospheric tale of doctor doing experimental brain surgery in remote English castle. Laughable."
Leonard Maltin, Classic Movie Guide.

Compiled by John M. Miller