Tony Randall appears in the audience at the second circus show.

Tony Randall related on a 1963 episode of Password All-Stars that his next film was called "The Circus of Dr. Lau," changed at some point before release to its eventual title.

Peter Sellers was the director's first choice to play Dr. Lao.

William Tuttle received an honorary Oscar for his makeup work on this film. It was the first one of two honorary Oscars awarded for makeup - the other one being John Chambers for Planet of the Apes.

According to a July 1962 LA Times item, Laurence Harvey was set to play the Tony Randall role.

According to a story that appeared in "Life" magazine Tony Randall had his head shaved for the part of Dr. Lao. When it was decided to have him appear in the audience as himself during the second show they could not find a wig that looked like his natural hair so they took a woman's wig and cut and styled it enough to get by for the few seconds he would be on screen.

Although it is now regarded as a classic fantasy film, this was a box office disappointment when it was first released. It caused a four-year gap before George Pal had his next film in theatres. It also marked that last time that Pal would direct.

Before it became apparent the film was not a hit, George Pal told press he was planning a sequel with Tony Randall recreating his role.

Oscar-winning soundtrack composer Leigh Harline worked for Disney from 1932-41 and wrote the music for some of the best-known Disney film songs, including "When You Wish Upon a Star", "I'm Wishing," "Whistle While You Work," "Heigh Ho," and "Some Day My Prince Will Come."

The "Fall of the City" spectacular that Dr. Lao presents as the grand finale of his circus contains much footage from an earlier George Pal production, "Atlantis, The Lost Continent" (1961)