A questionnaire study of Jamaican patients with homozygous sickle cell (SS) disease indicated a 42% prevalence of priapism, with a median age at onset of 21 years. Two predominantly different patterns of priapism were recorded: short "stuttering" episodes lasting less than three hours, with normal consequent sexual function, and severe prolonged attacks (generally more than 24 hours) commonly followed by impotence. Stuttering episodes were frequently a prodrome to a major attack. Over one fourth of those who had suffered priapism had some degree of impotence. Hematologic analysis indicated that priapism was significantly associated with low hemoglobin F levels and high platelet counts. Patients with severe attacks of priapism had lower hemoglobin F levels and reticulocyte count, and a higher mean corpuscular volume, than patients with only stuttering episodes. Priapism and impotence contribute to the morbidity of SS disease more frequently than previously recognized.