The Jamaican sickle cell cohort study, based on neonatal diagnosis of all cases of sickle cell disease among 100,000 consecutive births, has identified acute splenic sequestration (ASS) and pneumococcal disease as the most important complications in early life. The etiology of ASS is unknown and prophylaxis is therefore not possible. For first attacks, attention has been directed to parental education to achieve earlier diagnosis. Recurrent attacks may be prevented by prophylactic splenectomy. A controlled trial on the prevention of pneumococcal disease has indicated many pneumococcal septicemias in children given the 14 valent pneumococcal vaccine between the ages of 6 months and 3 years. No pneumococcal isolations occurred during the same period in children given monthly long-acting prophylactic penicillin. A controlled trial of folate supplementation for 1 year in children aged 6 months to 4 years indicated no difference between control and treatment groups in hemoglobin levels or weight and height velocity. The MCV was 4 fl less in the supplemented group. A controlled trial of feeder vessel photocoagulation in the therapy of proliferative retinopathy indicated significantly less vitreous hemorrhage in treated patients, but choroidal neovascularisation was a common complication of xenon arc therapy, and retinal tears commonly followed the use of the Argon laser. A new trial of scatter therapy is in progress.