A first comprehensive description of the clinical features of patients with the rare diagnosis of organic hallucinosis (OH) is presented, based on information from 11 OH patients among 14,889 patients who presented for evaluation over a 5-year period at our institution. This characterization is of particular current relevance to diagnosticians and clinicians because of the proposed major changes in the diagnostic system for OH in the upcoming DSM-IV and because of the virtual total lack of published information concerning this syndrome. This description includes a listing of the prevalence and mean severity of each symptom. The severity of the symptoms of OH are then compared with those of its crude "functional" equivalent of schizophrenia to determine which symptoms distinguish between these categories. Associated factors are also presented concerning demographics, modes of treatment, level of functioning, and current physical problems associated with OH.