PURPOSE: To characterize the racial differences in prognostic factors and treatment outcome for patients undergoing radiation therapy for carcinoma of the prostate. MATERIALS AND METHODS: From January 1975 through December 1989, 489 white and 157 black men with carcinoma of the prostate underwent irradiation. Factors analyzed were patient age, tumor stage and grade, prostate-specific antigen (PSA) levels, and disease-control and survival rates. RESULTS: More black patients than white patients were found to have poorly differentiated tumors. Black patients had higher PSA levels before and after treatment, resulting in a higher distant failure rate and poorer overall, cause-specific, and disease-free survival rates. CONCLUSION: Black men have more aggressive prostatic tumors, a higher rate of metastasis, and a poorer survival rate than do white men.