Background: Prostate cancer risk and mortality are higher in AAs versus CAUs. Post-hoc analyses of pooled Phase 3 data (n = 737) suggested substantial OS benefit for AA men receiving sipuleucel-T (n = 33) vs placebo (n = 10) (McLeod 2012). Compared with pooled placebo patients (n = 249), number needed to treat for OS benefit at 3 years was 3 for AAs and 8 for all sipuleucel-T-treated patients (n = 488) (Moses 2019). Herein we analyzed PROCEED (NCT01306890), a large real-world registry, in which all patients received sipuleucel-T. Methods: In PROCEED, 1902 mCRPC patients received ≥1 sipuleucel-T infusion. OS of all AA (n = 221) and CAU (n = 1649) men were compared. Baseline prostate-specific antigen (PSA), the most important prognostic variable for OS after sipuleucel-T (Schellhammer 2013), substantially differed by race. Thus, OS for a PSA-matched cohort (n = 219 AA; n = 438 CAU) was compared and univariable/multivariable analyses were performed. Post-sipuleucel-T use of OS-prolonging anticancer interventions was also assessed. Results: After a median follow-up of 46.6 mo, median OS was 35.2 (all sipuleucel-T-treated AAs) and 29.9 mo (all sipuleucel-T-treated CAUs): HR 0.81, 95% CI 0.68–0.97; P = 0.03. In the PSA-matched cohort, median OS was 35.3 and 25.8 mo, respectively (HR 0.70, 95% CI 0.57–0.86; P < 0.001). Sipuleucel-T-treated AAs with lower baseline PSA had markedly longer median OS vs sipuleucel-T-treated CAUs. Among those with ≤ median baseline PSA (29.48 ng/ml), median OS was 54.3 mo (AA) vs. 33.4 (CAUs); HR 0.52, 95% CI 0.37–0.72; p < 0.001. Along with other known prognostic factors, AA race was independently associated with prolonged OS on detailed multivariable analyses (HR 0.60, 95% CI 0.48–0.74; p < 0.001) and confirmed on sensitivity analyses. Post-sipuleucel-T life-prolonging anti-cancer therapies were balanced between groups. Conclusions: Sipuleucel-T-treated AAs had significantly improved OS vs sipuleucel-T-treated CAUs. This analysis marks the largest known racial difference in OS in response to any therapy for mCRPC, a finding with implications for both prostate cancer pathophysiology and cancer immunotherapy. Clinical trial information: NCT01306890