Prostate cancer is the most common non-cutaneous cancer and the second leading cause of cancer-related mortality among men in the USA. Growing evidence suggests that oxidative stress is involved in the development and progression of prostate cancer. In this study, the association between antioxidants from diet and supplements and biomarkers of oxidative stress in blood (n 278), urine (n 298) and prostate tissue (n 55) were determined among men from the North Carolina-Louisiana Prostate Cancer Project. The association between antioxidant intake and oxidative stress biomarkers in blood and urine was determined using linear regression, adjusting for age, race, prostate cancer aggressiveness and smoking status. Greater antioxidant intake was found to be associated with lower urinary 8-isoprostane concentrations, with a 10 % increase in antioxidant intake corresponding to an unadjusted 1·1 % decrease in urinary 8-isoprostane levels (95 % CI −1·7, −0·3 %; P value<0·01) and an adjusted 0·6 % decrease (95 % CI −1·4, 0·2 %; P value=0·16). In benign prostate tissue, thioredoxin 1 was inversely associated with antioxidant intake (P=0·02). No significant associations were found for other blood or urinary biomarkers or for malignant prostate tissue. These results indicate that antioxidant intake may be associated with less oxidative stress among men diagnosed with prostate cancer.