Denmark's first, and only (as of 2017), "giant monster" movie.

Two versions were filmed: a Danish-language version directed by Poul Bang, and an English-language version directed by producer Sidney W. Pink. All actors were in both versions, except Bodil Miller, who couldn't speak English. Marlies Behrens dubbed her character. AIP head Samuel Z. Arkoff said the dialogue had to be re-dubbed because he felt that the "sing-song Scandinavian accents" would have U.S. audiences laughing. Pink threatened to sue. After Pink had other industry professionals view his version of the film, the lawsuit was dropped and AIP released an edited, re-dubbed English-language version.

The paperback novelization, by Dean Owen, was peppered with gratuitous sexual content. Director/screenwriter Sid Pink was so enraged that he sued the publisher, Monarch Books.

The U.S. release features no opening credits.

A novelization of the film was published at the time of the film's release, as was a short-lived comic book series.

In AIP's English-language version, the farmer picked up and eaten by Reptilcus is played by Dirk Melchior, the 12-year-old son of writer Ib Melchior, who supervised the alterations for AIP's version.

Director Sidney Pink wanted to remake Reptilicus in 2001 to cash in on the success of Godzilla (1998). He died in 2002 before pre-production could begin.

Dirch Passer was a hugely popular comedic actor when this was filmed. At one point, the directors were going to call the film "Dirch and the Dragon."

Many elements were originally intended for Ib Melchior's aborted "Volcano Monsters" project.

Writer Ib Melchior dubbed several voices in the English-language version, including a reporter, a police officer, and a mayor.

Nora Hayden originally was slated to play Lise. She quit the project when she discovered that she would get second billing.

In one scene of a panicked crowd running through the streets of Copenhagen, a poster promoting a recital by British classical pianist Clifford Curzon is visible in the background.

In 1961, Charlton Comics produced a comic book based on the film. Reptilicus lasted two issues. After the copyright had lapsed, Charlton modified the creatures look and renamed it Reptisaurus. The series was now renamed Reptisaurus the Terrible and would continue from issue #3 before being cancelled with issue #8 in 1962. This was followed by a one-shot called Reptisaurus Special Edition in 1963.

The American version of Reptilicus was released on DVD on April 1, 2003 by MGM Home Entertainment under the Midnite Movies banner.[7] The Danish version was released on DVD from Sandrew Metronome in 2002. On June 16, 2015, the film was released in the Blu-ray format by Scream Factory as a double feature with the 1977 film Tentacles.