We investigated the prevalence of Parkinson's disease and other types of parkinsonism in a Sicilian population using a door-to-door two-phase approach. This design called for the administration of a brief screening instrument to all subjects who, on November 1, 1987, were residents of Terrasini (Palermo Province), Santa Teresa di Riva (Messina Province), and Riposto (Catania Province), Sicily (N = 24,496). Study neurologists using specified diagnostic criteria extensively investigated those subjects who screened positive. We found 63 subjects affected by Parkinson's disease, 21 with secondary parkinsonism, and seven with unspecified parkinsonism. The crude prevalence per 100,000 population was 371.5 for all types of parkinsonism and 257.2 for Parkinson's disease; for both entities, prevalence increased steeply with age and showed an inconsistent sex pattern. Our prevalence figures for Parkinson's disease are higher than those previously reported in Italy or elsewhere, which may be due, in part, to more complete case-ascertainment.