Background: Vitamin E, β-carotene, and vitamin C are micronutrient antioxidants that protect cells from oxidative damage involved in prostate carcinogenesis. In separate trials, supplemental vitamin E was associated with a decreased risk of prostate cancer among smokers and supplemental β-carotene was associated with a decreased risk of prostate cancer among men with low baseline plasma β-carotene levels. Methods: We evaluated the association between intake of these micronutrient antioxidants from foods and supplements and the risk of prostate cancer among men in the screening arm of the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. At baseline, trial participants completed a 137-item food frequency questionnaire that included detailed questions on 12 individual supplements. Cox proportional hazards models were used to estimate relative risks (RRs) and 95% confidence intervals (CIs). All statistical tests were two-sided. Results: We identified 1338 cases of prostate cancer among 29361 men during up to 8 years of follow-up. Overall, there was no association between prostate cancer risk and dietary or supplemental intake of vitamin E, β-carotene, or vitamin C. However, among current and recent (i.e., within the previous 10 years) smokers, decreasing risks of advanced prostate cancer (i.e., Gleason score ≥7 or stage III or IV) were associated with increasing dose (RR for >400 IU/day versus none = 0.29, 95% CI = 0.12 to 0.68; Ptrend = .01) and duration (RR for ≥10 years of use versus none = 0.30, 95% CI = 0.09 to 0.96; Ptrend = .01) of supplemental vitamin E use. Supplemental β-carotene intake at a dose level of at least 2000 μg/day was associated with decreased prostate cancer risk in men with low (below the median of 4129 μg/day) dietary β-carotene intake (RR = 0.52, 95% CI = 0.33 to 0.81). Among smokers, the age-adjusted rate of advanced prostate cancer was 492 per 100 000 person-years in those who did not take supplemental vitamin E, 153 per 100 000 person-years in those who took more than 400 IU/day of supplemental vitamin E, and 157 per 100 000 person-years in those who took supplemental vitamin E for 10 or more years. Among men with low dietary β-carotene intake, the age-adjusted rate of prostate cancer was 1122 per 100 000 person-years in those who did not take supplemental β-carotene, and 623 per 100 000 person-years in those who took at least 2000 μg/day of supplemental β-carotene. Conclusions: Our results do not provide strong support for population-wide implementation of high-dose antioxidant supplementation for the prevention of prostate cancer. However, vitamin E supplementation in male smokers and β-carotene supplementation in men with low dietary β-carotene intakes were associated with reduced risk of this disease.