The character of Karlsson is Astrid Lindgren's most popular character in Russia, even back in the days of the Soviet Union. In the 80s, Russian ambassador Boris Pankin told Astrid that the two books found in most Russian homes where "Karlsson-on-the-roof" and the bible. To which Astrid replied: "Oh, dear. I had no idea the bible was so popular".
Janne "Loffe" Carlsson, who plays the burglar Fille in this film, got so tired of Lars Söderdal running around the studio. Finally, Janne put the child actor on the floor and used a stapler to staple his clothes to the ground so he would lie still. This amused the director, Olle Hellbom, who got a bit nervous of Lars running around.
In the books, Kalrssons pants are blue but are changed to a more gray hue in the film. This is because of the blue screen effect used for the flying scenes, and had the pants been blue they would've been completely obliterated in the process. A similar thing happened when they shot the Pippi Långstrump TV-series and two movies.
There was originally going to be more than one movie based on the "Karlsson-on-the-roof" series of novels, but this film performed quite poorly at the box office and so it was decided against that. The producer, Olle Nordemar, gave another reason in that all Karlsson books share the same structure and it wouldn't be any fun in doing the same film, over and over again.
This is the only Astrid Lindgren adaptation produced in the 1970s and '80s in which actor Allan Edwall does not appear.