Objectives: It is known that African American men have a greater risk of prostate cancer than white men. We investigated whether this was true for first-generation black Caribbean and black African men in the United Kingdom. Methods: A clinical cohort study design recruiting all cases of prostate cancer diagnosed over a 5-yr period and residing in defined areas of London and Bristol. We calculated the age-standardised incidence rates and relative risk for all black men, and black Caribbean and black African men versus white men. Results: Black men had higher age-adjusted rates of prostate cancer (166 per 100,000, 95% confidence interval [95%CI], 151-180 per 100,000) than white men (56.4 per 100,000, 95%CI, 53.3-59.5 per 100,000). The relative risks for all black, black Caribbean, and black African men were 3.09 (95%CI, 2.79-3.43; p < 0.0001), 3.19 (95%CI, 2.85-3.56; p < 0.0001) and 2.87 (95%CI, 2.34-3.53; p < 0.0001), respectively. There was no strong evidence that the rates for black Caribbean differed from black African men. The higher risk in black men compared with white men was more apparent in younger age groups (p value for interaction <0.001). Conclusions: Black men in the United Kingdom have substantially greater risk of developing prostate cancer compared with white men, although this risk is lower than that of black men in the United States. The similar rates in black Caribbean and black African men suggest a common genetic aetiology, although migration may be associated with an increased risk attributable to a gene-environment interaction.