Delusional misidentification syndromes (DMS) are beginning to be well described clinically but little is known about their epidemiology. To try and obtain an estimate of their prevalence, a survey was performed of all admissions to a locked psychiatric inpatient unit from April 1983 to June 1984. 26 patients satisfied clinical criteria for DMS during this time and overall 835 patients were admitted to the unit. Thus, a crude prevalence of 3.1% was found. The median age of the patients was 29 years. The overwhelming majority had a principal psychiatric diagnosis of paranoid schizophrenia and only 2 of an affective disorder. By a small margin, most patients were male. The implications and limitations of these findings are discussed.