The excess risk of diabetic complications in African Americans may be due to poor glycemic control arising from suboptimal use and/or quality of diabetes-related health care. However, little is known about racial differences in these factors, particularly in urban populations. We conducted a cross-sectional study using medical claims and encounter data on 1,106 adults with diabetes aged > or =30 years who were members of an urban managed care organization in capitated health plans. We examined health care and routine hemoglobin A(1c) (HbA(1c)) testing in a biracial cohort for 12 months. We then followed individuals for an additional 12 months, using a retrospective cohort design, to determine how this health care predicted subsequent emergency room visits. On average, compared with their white counterparts, African Americans had fewer primary care visits (85% vs. 91% with four or more visits) and fewer HbA(1c) tests (56% vs. 68% with two or more HbA(1c) tests) (all P < 0.05). Likewise, in the subset who underwent one or more HbA(1c) measurement (n = 855), African Americans displayed poorer glycemic control (HbA(1c) 9.1 +/- 2.9%) than whites (8.5 +/- 2.2%; P = 0.001). In multivariate analyses, racial differences in visit frequency and HbA(1c) testing were attenuated by adjustment for age, sex, and type of capitated plan and did not remain statistically significant. The relationship of health care to subsequent emergency room visits differed by race; in African Americans, fewer primary care visits and HbA(1c) tests predicted greater risk of emergency room visits. Even in a capitated, managed care setting, urban African Americans with diabetes are less likely than their white counterparts to undergo routine primary care visits and laboratory testing and are more likely to have suboptimal glycemic control. Differences in age, sex, and insurance type seemed to explain some of the disparities. Future research should determine the individual contributions of physician, patient, and system factors to the racial disparities in health care.