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PURPOSE: African-Americans have a higher age-adjusted incidence and a higher disease-specific mortality than whites. Two potential causes are differences in biology or socioeconomic status, the latter leading to differences in access, delivery, or utilization of health care. In this study, we compare serum prostate-specific antigen (PSA) levels for comparable stage and grade-disease, as well as individual insurance status. PSA is a demonstrated indicator of the size and virulence of tumor and is correlated with prognosis. Insurance status has been linked with income and education and is an indicator of access to medical care. PATIENTS AND METHODS: All patients were referred to the University of Chicago Center for Radiation Therapy (UCCRT) with stages A-C (T1-4) prostate cancer. They were seen in four different facilities, designated A through D, and were evaluated and staged by the faculty of UCCRT using the same criteria. Hospitals A and B are large teaching hospitals located within the city of Chicago; C and D are suburban and urban community hospitals, respectively. A total of 341 patients seen between May 1987 to November 1992 are included in this study. RESULTS: In univariate analysis, PSA levels were significantly associated with stage, grade, and race. Higher mean PSA levels were seen with increasing clinical stage and grade. African-Americans had higher mean values than whites. Private insurance and managed care patients had lower values than Medicare-only patients. Within each race, the above results were reproduced, except for insurance status, which was significant only in African-Americans. In multivariate analysis, stage, grade, and insurance status were significant in African-Americans, whereas only stage and grade were significant in whites. Within comparable insurance status, stage, and grade, no racial differences were found, except among Medicare-only patients, with African-Americans who had stage B or grade 2 disease having higher mean PSA levels than whites. Racial differences were seen at hospital B, but not at hospital A. No racial comparisons could be made at hospitals C or D due to an insufficient number of African-American patients. At hospital A, whites and African-Americans had comparable private plus HMO insurance distributions (81.1% and 86.9%, respectively); at hospital B, the distribution was quite different--only 4.4% of whites had Medicare-only insurance while 31.8% African-Americans had no supplementary insurance. For all patients in the multivariate analysis, racial difference was seen only among Medicare-only patients. CONCLUSIONS: Our results suggest that socioeconomic differences are responsible for the racial differences noted in prostate cancer. Our findings of higher PSA levels in African-American Medicare-only patients may result from the many African-Americans disproportionately uninsured throughout their lives compared with whites and thus using services at later stages of disease. A second possible explanation is cultural or ethnic differences in care-seeking behavior, with poorer African-Americans less likely to pursue care for disease until it has progressed. Our findings can explain the dichotomy of poorer overall outcome among African-Americans with prostate cancer, but comparable stage-adjusted outcome with comparable treatments between African-Americans and whites.