Animal and in vitro models of prostate cancer demonstrate high IL-10 levels result in smaller tumors, fewer metastases, and reduced angiogenesis compared to controls. We sought to examine the hypothesis that genotypes correlated with low IL-10 production may be associated with increased prostate cancer risk among Finnish male participants from the Alpha-tocopherol Beta-carotene Cancer Prevention Study. DNA from 584 prostate cancer cases and 584 controls was genotyped for four IL-10 alleles, -1082, -819, -592, and 210. DNA from more of the controls than cases failed to amplify, resulting in 509 cases and 382 controls with genotype data for -1082; 507 and 384 for -819; 511 and 386 for -592; and 491 and 362 for 210. Odds ratios for the association between the IL-10 genotypes and risk of prostate cancer or, among cases only, high-grade disease were calculated using logistic regression. In this population, the -819 TT and -592 AA low expression genotypes were highly correlated. These two genotypes also were associated with increased prostate cancer susceptibility (OR = 1.92, 95% CI 1.07-3.43 for -819) and, among cases, with high-grade tumors (OR = 2.56, 95% CI 1.26-5.20 for -819). These data demonstrate genotypes correlated with low IL-10 production are associated with increased risk of prostate cancer and with high-grade disease in this population.