Previous studies have shown high rates of schizophrenia among the Afro-Caribbean population in Britain. In order to assess the role of genetic factors in the aetiology of this phenomenon, we have used a standardised family history method (FHRDC) to compare lifetime morbidity risks for first-degree relatives of Afro-Caribbean and white patients with RDC schizophrenia admitted in Central Manchester between 1982 and 1988. Lifetime morbidity risk for parents of Afro-Caribbean subjects was 8.9%, and for parents of white patients 8.4%. For the siblings of black probands, however, the risk was 15.9%, as compared with 1.8% for white siblings (P < 0.05). Among siblings of UK-born Afro-Caribbean probands, morbid risk was even higher at 27.3% (P = 0.001). High rates among siblings of younger Afro-Caribbean patients are consistent with previous reports of a higher incidence in the UK-born. These observations suggest that schizophrenia among Afro-Caribbeans is no less familial than for the remainder of the population, but that the increased frequency of the disorder is due to environmental factors which are most common in the Afro-Caribbean community, and capable of precipitating schizophrenia in those who are genetically predisposed.