Beatrice Lillie's last film. She was showing early signs of Alzheimer's disease, and had trouble memorizing her lines. During filming, Julie Andrews stood off-camera and repeated Lillie's lines to her, so Lillie could complete her scenes.
Mary Tyler Moore said that she always thinks of the tap dancing scene in this film whenever she sees an elevator.
According to Mary Tyler Moore's autobiography "After All", Lew Wasserman had brought her to Universal after her unexpected success as a comic actress on The Dick Van Dyke Show with the hopes of making her "the next Doris Day" in light movie comedies. This was originally intended to be a film of that type until Julie Andrews came onboard, and only then did it become a musical that focused more on her. Also, Moore originally had a solo song that was cut from the final release.
Film debut of Pat Morita.
The film was based on the British musical "Chrysanthemum", which opened in London in 1956.
The stage musical "Thoroughly Modern Millie" opened at the Marquis Theater on April 18, 2002, ran for 903 performances and won the 2002 Tony Award (New York City) for the Best Musical and was nominated for Best Book and Score.