Doris Day's costumes for this film were created by Irene, a well-known, single-named designer who received her second Oscar nomination for her work here. Two years after working on Midnight Lace, Irene committed suicide, jumping from an upper-floor window of Hollywood's Knickerbocker Hotel.
Doris Day vowed to never make another thriller after this movie, claiming it emotionally drained her. She stayed true to her word; until her retirement eight years later, the only movies she made were comedies.
In her autobiography, Doris Day wrote that to prepare herself for one of the terror scenes, she recalled a time when her first husband, trombonist Al Jorden, dragged her out of bed when she was ill and pregnant and hurled her against a wall. Day related that in the scene she wasn't acting hysterical, she was hysterical, and at the end of the take, she collapsed in a real faint. She was carried to her dressing room, and Producer Ross Hunter shut down production for a few days while she recovered.
The white gown that Doris Day wore is the same dress she wore to The 32nd Annual Academy Awards (1960), where she was Oscar-nominated for her performance in Confidences sur l'oreiller (1959).
Dictating his memoirs near the end of his life, Sir Rex Harrison barely mentioned this movie, except to say that he wasn't fond of the script. He also (falsely) reported that Doris Day was under so much pressure to make the picture work that she collapsed. Day was indeed under strain, though it was due to her personal form of method acting that caused her breakdown, not from the script or the production.