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The working titles of this film were Christmas in Paradise and The Magnificent Brat. Although copyright records for Kathy O list the copyright registration date as May 17, 1957, the film's registration number, LP12460, indicates that the correct date should be May 17, 1958, just prior to the film's release. An July 8, 1957 Hollywood Reporter item mistakenly identifies Howard Pine as the producer and Borden Chase as screenwriter. According to the Hollywood Reporter review, "Harry Johnson" was based on Universal's "mild-mannered and efficient" publicist, Dan Thomas. The Variety review notes that photographs of Universal stars adorn the walls of the "Western National" studio in the film.
According to a July 1958 Hollywood Reporter news item, Mack Sennett filed protests with Universal and the MPAA stating that the title Kathy O' was too similar to the title of his 1920 film Molly O', which he reactivated in 1940 and planned to remake. The disposition of the suit is unknown.
June and July 1957 Hollywood Reporter news items add the following members to the cast: Frank Woolf, Peter Dane, Betty Harford, Stanley Fafara, Ricky Allen, Tristam Coffin, Mary Alan Hokanson, Billy Lally, Smoky Whitfield, Martin Smith, Syl Lamont, Leon Culker, Bill Anders, John Phillips and Harold Bostwick. Their appearance in the final film has not been confirmed. Kathy O' marked the feature film debut of Mary Jane Croft.