Clinical features and potential risk factors for chronic leg ulceration (duration >6 months) in homozygous sickle cell (SS) disease were examined in 225 subjects in the Jamaican Cohort Study. Potential risk factors included the number of HBA genes, steady state haematology, serum lactate dehydrogenase (LDH), venous incompetence, and socio-economic status. Chronic ulcers occurred in 53 subjects with the highest risk of ulcer development at 18 years. The prevalence was 29·5% and cumulative incidence 16·7%. Gender or a-thalassaemia trait did not affect the incidence of leg ulcer. Ulceration was associated with lower haemoglobin, red cell count, fetal haemoglobin, and socio-economic status and higher reticulocyte count, platelet count, serum LDH and venous incompetence in univariate analyses. Venous incompetence [Hazard Ratio (HR) 3·0–4·0] and socio-economic status (HR 0·8) were most consistently associated with leg ulceration on multivariate analysis. Regression models incorporating serum LDH suggested this to be a stronger predictor than haematological indices. The prevalence of ulcers at 30% is less than previous estimates in Jamaica, probably reflecting the lack of ascertainment bias in the Cohort Study, and also a real secular decline. In Jamaica, venous incompetence, low socio-economic status, and high serum LDH were the strongest predictors of chronic ulceration.