Background and Purpose—The morbidity and mortality of subarachnoid hemorrhage (SAH) are high, and established risk factors are scarce. We prospectively assessed the association of blood pressure, smoking, and body mass with the risk of aneurysmal SAH.

Methods—All residents 20 years were invited to the Nord-Trøndelag Health (HUNT) Study (1984 to 1986) and 74 977 (88.1%) attended. The study included standardized measurements of blood pressure, body weight and height, and self-administered questionnaires. Participants who later had aneurysmal SAH (n=132) were identified, and hazard ratios (HRs), adjusted for age and sex, were estimated using Cox regression analysis.

Results—The crude annual incidence of aneurysmal SAH was 9.9 per 100 000 people; the incidence was almost twice as high in women as in men (12.9 versus 6.8, P=0.001). Systolic blood pressure was positively associated with risk (P for trend=0.001). Compared with the reference (<130 mm Hg), the adjusted HR in people with systolic blood pressure of 130 to 139 mm Hg was 2.3 (95% CI, 1.4 to 3.8) and for systolic blood pressure >170 mm Hg, the HR was 3.3 (95% CI, 1.7 to 6.3). Diastolic pressure showed similar positive associations. Compared with never smokers, former (HR, 2.7; 95% CI, 1.4 to 5.1) and current (HR, 6.1; 95% CI, 3.6 to 10.4) smokers had substantially higher risk. Compared with normal weight (body mass index, 18.5 to 24.9 kg/m²), overweight people were at lower risk (HR, 0.6; 95% CI, 0.4 to 1.0).

Conclusions—Systolic and diastolic blood pressure were strong predictors of aneurysmal SAH, and there was a substantially increased risk associated with smoking. However, high body mass was associated with reduced risk of aneurysmal SAH.