Background and Purpose— The high incidence of aneurysmal subarachnoid hemorrhage (aSAH) in Finland may be related to genetic or environmental factors, which may also influence patient and aneurysm characteristics. We compared these characteristics in 2 cohorts in Finland (Kuopio) and the Netherlands (Utrecht). Methods— For aSAH patients in Kuopio (n=1786) and Utrecht (n=1788), we compared sex, age at onset, and the sites and number of aneurysms from 1986 to 2005. Five-year time trends were assessed with χ 2 tests (sex distribution and the sites and number of aneurysms) and with 1-way ANOVA (age). Results— The proportion of men in Kuopio (46.1%; 95% CI, 43.8% to 48.4%) was higher than in Utrecht (33.6%, 95% CI, 31.4% to 35.8%) and declined in Kuopio from 50.9% (95% CI, 46.3% to 55.5%) in 1986–1990 to 42.8% (95% CI, 38.0% to 47.6%) in 2001–2005. Mean±SD age at onset was 52.4±13.3 years in Kuopio and 53.3±14.3 years in Utrecht. Both increased similarly over time. The most common aneurysm site in the Kuopio cohort was the middle cerebral artery (33.1%; 95% CI, 30.9% to 35.3%) and in the Utrecht cohort was the anterior communicating artery (38.0%; 95% CI, 35.5% to 40.5%). Multiple aneurysms were more frequent in Kuopio (27.8%; 95% CI, 25.1% to 29.2%) than in Utrecht (14.8%; 95% CI, 13.0% to 16.6%). Sites and proportions of multiple aneurysms did not change during 1986–2005. Conclusions— The cohorts of aSAH patients differed with respect to age at onset and the number and sites of aneurysms. The decline in the proportion of men in Kuopio coincided with increased smoking and alcohol use in women and decreased smoking in men. The differences in aneurysm characteristics remained stable, which suggests that these factors are less influenced by environmental factors.