The annual incidence rate of primary intracerebral hemorrhage (ICH) in Izumo City, Japan, appears to be the highest rate among those reported. Despite improvement of management and surgical therapy, the overall morbidity and mortality after ICH are still high. The author investigated the risk factors for ICH in patients in Izumo. A case-control study of 242 patients (137 men and 105 women with ages ranging from 34 to 97 years) with primary ICH was conducted in Izumo between 1991 and 1998. Hypertension, diabetes mellitus, heart disease, liver disease, alcohol consumption, cigarette smoking, and serum levels of total cholesterol, aspartate aminotransferase, and alanine aminotransferase were assessed as possible risk factors for ICH by using conditional logistic regression. The prevalence of hypertension among ICH patients was 77% and the odds ratio (OR) for hypertension was 17.07 (95% CI: 8.30-35.09), which are much higher than figures reported from Western countries. The OR for hypertension was higher in individuals < or = 69 years of age than in those > or = 70 years of age and lower for lobar hemorrhage than for hemorrhages at other sites. High serum total cholesterol (> or = 220 mg/dl) was the second most important risk factor for ICH (OR: 2.52; 95% CI: 1.23-5.14), and low total cholesterol (< 160 mg/dl) decreased the risk of ICH (OR: 0.47; 95% CI: 0.27-0.82). In contrast, heart disease decreased the risk of ICH, and there was no observed association between alcohol consumption, cigarette smoking, or diabetes mellitus and ICH. This study conducted in Izumo suggests that hypertension is the most important risk factor for ICH and contrary to most previous studies indicates that serum total cholesterol concentration is also positively associated with the risk of ICH. In contrast, heart disease may decrease the risk of ICH.