The presence of a chronically ill family member may adversely affect the psychological health of siblings. This study used the General Health Questionnaire and the Modified Social Adjustment Scale to assess psychological distress in 20 younger siblings (4 AA, 16 AS genotypes), aged 16-19 years, of patients with homozygous sickle cell (SS) disease. The results were compared with those previously obtained in the 20 older siblings with SS disease and in 89 controls with a normal haemoglobin (AA) genotype. High levels of psychological distress occurred among all three groups. Greater psychological distress and poorer social adjustment occurred among siblings compared to AA controls but these differences disappeared after adjusting for the reduced age of siblings. The two measures were similar in SS patients and AA controls. The level of psychological distress among siblings of SS patients did not differ from that in SS patients or AA controls.