Race and sex differences have been reported in the prevalence of complications from insulin-dependent diabetes mellitus (IDDM). Because metabolic control is assumed to be associated with the probability of developing future complications, race and sex differences in metabolic control were assessed in a group of adolescents. Subjects were 27 Black and 27 White adolescents who were similar in age, age at diagnosis, and social class. Girls did not differ on number of days since their last menses. A 2-by-2 (race-by-sex) analysis of variance revealed that the Black female group had worse HbA1c than each of the other groups (P less than .012). Multivariate analyses of variance were conducted to determine whether the poor metabolic control of the Black girls was associated with pertinent psychosocial variables. The analyses revealed that their poor control was not associated with a deficiency in the girls' knowledge about IDDM, adherence to treatment, self-concept, coping patterns, family functioning, stress, social support, or involvement in the health-care system. If the poor control of the Black girls is not associated with psychosocial deficiencies, biological variables or psychosocial variables not assessed in this study are probably operative.