Sleep terrors and sleepwalking are described as arousals from slow wave sleep with no or poor mental recollection. To characterize the mental content retrospectively associated with sleep terrors or sleepwalking. University Hospital. Controlled prospective cohort. Forty-three patients referred for severe sleepwalking/sleep terrors (age: 26 +/- 7 y, 46% men, 5 with sleep terrors only, 8 with sleepwalking only, and 30 with both), matched with 25 healthy control subjects. Thirty-eight of the 43 patients (88%) underwent an interview about the frequency, time, behaviors, and mental content associated with the episodes of sleepwalking and sleep terrors, whenever they occurred over a lifetime. The mental contents were classified for complexity (Orlinski score), and for characters, emotions, fortune/misfortune, and social interactions (Hall and Van de Castle categories). Patients and control subjects underwent an overnight video-polysomnogram. Seventy-one percent of the patients reported at least 1 dreamlike mentation associated with the sleepwalking/sleep terrors episode. The dreamlike mentation action corresponded with the observed behavior. A total of 106 dreamlike mentations were collected (mean: 3 +/- 3.4 dreamlike mentations/patient, range 0-17). Most (95%) dreamlike mentations consisted of a single visual scene. These dreamlike mentations were frequently unpleasant, with aggression in 24% (the dreamer being always the victim), misfortune in 54%, and apprehension in 84%. The patients with dream mentations reported more severe daytime sleepiness. Short, unpleasant dreamlike mentations may occur during sleepwalking/sleep terrors episodes, suggesting that a complex mental activity takes place during slow wave sleep. Sleepwalking may thus represent acting out of the corresponding dreamlike mentation.