OBJECTIVE: We examined whether there were racial differences in initial treatment for clinically localized prostate cancer and investigated whether demographic, socioeconomic, clinical, or tumor characteristics could explain any racial differences. DESIGN: Prospective cohort study. SETTING: Population-based tumor registries in Connecticut, Los Angeles, and Atlanta. PARTICIPANTS: We evaluated 1144 African-American and non-Hispanic white men, aged 50 to 74 years, with clinically localized cancer diagnosed between October 1994 and October 1995. MEASUREMENTS AND MAIN RESULTS: We obtained demographic, socioeconomic, and clinical data from patient surveys and medical record abstractions. We reported adjusted percentages for receiving treatment derived from multinomial logistic regression. We found an interaction between race and tumor aggressiveness. Among men with more aggressive cancers (PSA > or = 20 ng/mL or Gleason score > or = 8), African Americans were less likely to undergo radical prostatectomy than non-Hispanic whites (35.2% vs 52.0%), but more likely to receive conservative management (38.9% vs 16.3%, P=.003). Among the 71% of subjects with less aggressive cancers, African Americans and non-Hispanic whites were equally likely to receive either radical prostatectomy or radiation therapy (80.0% vs 84.5%, P=.2). CONCLUSIONS: African Americans with more aggressive cancers were less likely to undergo radical prostatectomy and more likely to be treated conservatively. These treatment differences may reflect African Americans' greater likelihood for presenting with pathologically advanced cancer for which surgery has limited effectiveness. Among men with less aggressive cancers-the majority of cases-there were no racial differences in undergoing radical prostatectomy or radiation therapy.