OBJECTIVE: There are no reliable data on the prevalence of multiple personality disorder. The objective of the study was to determine whether and, if so, how frequently patients with multiple personality disorder are encountered and diagnosed in Switzerland. METHOD: All qualified Swiss psychiatrists were sent a questionnaire on multiple personality disorder along with the DSM-III description of multiple personality disorder and three case examples. A total of 836 psychiatrists (66%) answered after two mailings, and 770 questionnaires qualified for evaluation. In addition, a random sample of nonresponders were contacted by telephone. RESULTS: Three percent of the psychiatrists indicated that, at the time of the inquiry, they were treating or examining one or more patients who met DSM-III criteria for multiple personality disorder, and 10% indicated that they had seen multiple personality disorder at least once during their professional career. The patients were not equally distributed among the psychiatrists; three colleagues reported that they had seen much higher numbers of patients with multiple personality disorder. The point prevalence of multiple personality disorder among patients seen by psychiatrists in Switzerland amounts to 0.05%-0.1%. CONCLUSIONS: Multiple personality disorder appears to be a disorder that genuinely exists, even though it occurs relatively rarely.