A questionnaire was designed which made specific enquiries about peri-operative nightmares and general enquiries regarding peri-operative hallucinations, sleep disturbance and pain. The questionnaire was completed by four groups of patients. Groups 1 and 2 comprised patients who had undergone elective cardiac surgery and major noncardiac surgery respectively. Group 3 comprised patients undergoing day surgery. Group 4 consisted of 100 randomly selected patients who had undergone minor elective surgery to the upper or lower limbs during the preceding 2 years, half of whom had received regional and half general anaesthesia. Two hundred and seventy-one completed questionnaires were analysed. In all, 18.5% of patients had experienced at least one nightmare during the postoperative week and and the highest incidence (27.9%) was found in group 1. Nightmares occurred most commonly on the fourth postoperative night and did not correlate with disturbed sleep, hallucinations or any other symptom recorded. Patients in group 1 reported the highest incidences of disturbed sleep (54.8%) and hallucinations (12.5%).