Objective: The purpose of this study was to investigate sex differences in the major established risk factors for aneurysmal subarachnoid hemorrhage (aSAH) in a large, population-based cohort. Methods: Sex differences in the established risk factors for aSAH (smoking, hypertension, and alcohol consumption) were examined in a prospective, population-based cohort consisting of 92,462 participants of the Nord-Trøndelag and the Tromsø Health Studies in Norway. Results: We identified 120 cases of aSAH during 1,002,148 person-years at risk. Compared with the risk in nonsmokers, the risk of aSAH was higher in current cigarette-smoking women than in men (hazard ratio = 8.9, 95% confidence interval [CI] 4.7-17.0 vs hazard ratio = 2.8, 95% CI 1.3-6.1, after adjustment for age and alcohol consumption). The interaction between sex and current smoking was present on an additive scale (relative excess risk due to interaction 3.1, 95% CI 0.5-5.8), indicating a higher risk of aSAH associated with current cigarette smoking in women than in men. No sex differences in the risk of aSAH were observed with respect to hypertension or alcohol consumption. Conclusions: This prospective, population-based cohort study showed that compared with the risk in nonsmokers, the risk of aSAH was higher in current cigarette-smoking women than in men. This finding may at least partially explain the gender gap in aSAH incidence. A more intensive smoking cessation intervention should be considered in women at risk of aSAH.