Uric acid is a potent antioxidant and thus might protect against cancer. To test this hypothesis, we examined the relationship of serum uric acid to subsequent cancer incidence in a cohort of Japanese men in Hawaii. The study population consisted of 7889 men identified in the years 1965-1968 and followed by active hospital surveillance through November 1991. Cancer risk by serum uric acid level was analyzed using Cox proportional hazards regression with adjustment for age and, where indicated, smoking, alcohol use, and body mass index. No significant associations were seen for total cancer (1544 cases), or for cancers of the stomach (214), colon (272), rectum (105), lung (223), bladder (89), or hematopoietic system (77). For prostate cancer (293 cases), a positive association was found (relative risk for highest versus lowest quartile of serum uric acid = 1.5; 95% confidence interval 1.1-2.1; p for trend = 0.04). When the interval from examination to diagnosis was considered, this association was strongest for cases diagnosed in the first 10 years, was attenuated after 15 years, and disappeared completely after 20 years. The findings from this study do not support the hypothesis that uric acid protects against cancer occurrence.