Observational data suggest that diets rich in fruits and vegetables and with high serum levels of antioxidants are associated with decreased incidence and mortality of stroke. We studied the effects of alpha-tocopherol and beta-carotene supplementation. The incidence and mortality of stroke were examined in 28 519 male cigarette smokers aged 50 to 69 years without history of stroke who participated in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study (ATBC Study). The daily supplementation was 50 mg alpha-tocopherol, 20 mg beta-carotene, both, or placebo. The median follow-up was 6.0 years. A total of 1057 men suffered from incident stroke: 85 men had subarachnoid hemorrhage; 112, intracerebral hemorrhage; 807, cerebral infarction; and 53, unspecified stroke. Deaths due to stroke within 3 months numbered 38, 50, 65, and 7, respectively (total 160). alpha-Tocopherol supplementation increased the risk of subarachnoid hemorrhage 50% (95% CI -3% to 132%, P=0.07) but decreased that of cerebral infarction 14% (95% CI -25% to -1%, P=0.03), whereas beta-carotene supplementation increased the risk of intracerebral hemorrhage 62% (95% CI 10% to 136%, P=0.01). alpha-Tocopherol supplementation also increased the risk of fatal subarachnoid hemorrhage 181% (95% CI 37% to 479%, P=0.01). The overall net effects of either supplementation on the incidence and mortality from total stroke were nonsignificant. alpha-Tocopherol supplementation increases the risk of fatal hemorrhagic strokes but prevents cerebral infarction. The effects may be due to the antiplatelet actions of alpha-tocopherol. beta-Carotene supplementation increases the risk of intracerebral hemorrhage, but no obvious mechanism is available.