The effects of long-term aspirin for the treatment of sickle cell disease were compared with placebo in a double-blind trial completed by 29 patients. Each patient was submitted to a 5-month period of treatment with aspirin (median dose 31 mg/kg/day) and an equivalent period with placebo. No clinical or laboratory differences were observed between the two phases, including the frequency of painful crises and infectious episodes, hemoglobin concentration, PCV, reticulocytes, Hb F, bilirubin, irreversibly sickled cells, filterability of red cell, sickling in vitro and hypoxia-induced potassium loss.