Cohen was especially a fan of director Michael Curtiz, whose films include The Adventures of Robin Hood, Casablanca, and Dodge City.

Other writing credits during the 1950s and 1960s included the fantasy-suspense anthologies Kraft Television Theatre (1958) and Kraft Suspense Theatre (1965), the espionage TV series Blue Light (1966) starring Robert Goulet and Coronet Blue (1967) starring Frank Converse, and the science-fiction TV series, The Invaders (1967–1968).

His directorial debut was the 1972 comedy film Bone (aka Beverly Hills Nightmare) starring Yaphet Kotto.

He wrote, produced and directed the horror film It's Alive, about a mutant monster baby that embarks on a killing spree.

He concentrated his work predominantly within the horror genre throughout the 1970s and 1980s, often incorporating elements of crime, police procedural, and science fiction with scathing social commentary.

[7] The emphasis in It's Alive is on the potential effects of chemicals to the ecosystem, and experimental prescription drugs that can be harmful to unborn babies.

The score for It's Alive was composed by Bernard Herrmann, known for his contributions to many Alfred Hitchcock films, including Psycho, North by Northwest, and Vertigo.

During the 1980s, Cohen directed, produced, and scripted a number of low-budget horror films, many of which featured actor Michael Moriarty.

The cast is headed by Moriarty and co-stars David Carradine, Candy Clark, Richard Roundtree, and James Dixon (another Cohen regular).

David "Mo" Rutheford, an industrial saboteur, played by Moriarty, is hired to investigate the origins of the Stuff and decides to destroy the product.

Throughout the decade Cohen was further involved in various TV projects including NYPD Blue and the Ed McBain-inspired 87th Precinct: Heatwave.

Cohen's output after the 1990s was less prolific and concentrated solely on scriptwriting, except for a brief return to directing with the Masters of Horror episode "Pick Me Up" (2006).

His first project, Phone Booth (2002), became involved in a Hollywood bidding war, the script eventually ending up in the hands of Joel Schumacher.

The film starred Colin Farrell, Katie Holmes, Kiefer Sutherland, and Forest Whitaker; it was produced by David Zucker.

Cohen nevertheless received acclaim for the above-mentioned Pick Me Up, which he directed for the Mick Garris TV series Masters of Horror (2006).

In 2003, Cohen, together with production partner Martin Poll, was at the center of a lawsuit against 20th Century Fox, claiming the company had intentionally plagiarized a script of theirs titled Cast of Characters in order to create the Sean Connery-starring League of Extraordinary Gentlemen in 2003.

'[9][10][11] The League of Extraordinary Gentlemen was an adaptation of the 1999 published comic book series by Alan Moore and artist Kevin O'Neill.

[12] In 2006, Cohen was included in the Masters of Horror TV anthology, which also included – but was not limited to – writers and directors as diverse as Dario Argento, Clive Barker, John Carpenter, Richard Chizmar, Don Coscarelli, Wes Craven, David Cronenberg, Joe Dante, Guillermo del Toro, Ernest Dickerson, Stuart Gordon, James Gunn, Sam Hamm, Tom Holland, Tobe Hooper, Lloyd Kaufman, Mary Lambert, John Landis, Joe R. Lansdale, Bentley Little, H.P.

Lovecraft, Joe Lynch, William Lustig, Peter Medak, Lucky McKee, Kat O' Shea, Robert Rodriguez, Eli Roth, David Schow, and Tim Sullivan.

[16] Cohen offered his 1974 script but remarks that it was completely ignored: "I would advise anybody who likes my film to cross the street and avoid seeing the new enchilada.

[19] The Apollo Movie Guide remarks that The Stuff works on a purely visceral level, and that it further achieves a tongue-in-cheek social parody of a society that cannot help buying into the latest craze.

[24] Horror author and movie critic, Kim Newman, praises Cohen's plot originality and canny use of characters in Empire, pointing out the director's use of an oddball as lead – Jimmy Quinn – who would ordinarily be a secondary character or warrant solely a cameo appearance; Newman also explains how Cohen has relegated all the usual plot devices – in movies such as King Kong – to the background.

[26] The New York Times, following the film's opening day at the Rivoli Theater, had just 'a few words – only a very few – about Q, offering a brief neutral synopsis and a couple of quotes.

"[29] Black Hole magazine opines that despite a lack of A-List actors and special effects, It's Alive still manages to maintain the viewer's interest due to Cohen's "unique horror concept and a script rich in ideas."

The magazine continues, however, to comment on Cohen's lack of patience and drive when completing his movies, regarding the end products as being "hastily thrown-together" and "a mosaic of scenes, rather than a satisfying whole."

"[32] CinePassion online magazine simply states: "[a] work of genius, in other words, possibly the Cohen joint that brims with the most all-pervasive invention and danger, as radical a Seventies 'incoherent text' as Taxi Driver and a clear linchpin of The X-Files.

"[34] But Time Out applauded Cohen for offering "the perfect existential anti-hero" in New York cop, Lo Bianco, in a film that "overflows with such perverse and subversive notions that no amount of shoddy editing and substandard camerawork can conceal [its] unusual qualities" and that by "[d]igging deep into the psyche of American manhood, it lays bare the guilt-ridden oppressions of a soulless society.