Patients with mild to moderate essential hypertension were treated mainly with an ACE inhibitor (delapril, n=980) or a Ca antagonist (n=956) for 12 months, and the incidence of cerebrovascular and cardiovascular events as well as drug-related side effects were compared between the two groups. There were no significant differences between the clinical backgrounds of the two groups. In both groups, the blood pressure was decreased significantly from 1 month of treatment onwards, with the degree of reduction being greater in the Ca antagonist group throughout the study period (p<0.001). Cerebrovascular or cardiovascular events occurred in 11 out of 980 patients in the delapril group and 18 out of 956 patients in the Ca antagonist group (p=NS). Cerebrovascular disease developed in 5 delapril-treated patients and 11 Ca antagonist-treated patients, and heart disease developed in 5 and 7 patients, respectively (both p=NS). Discontinuation of treatment due to side effects was significantly more common in the delapril group than in the Ca antagonist group (p<0.001). There was no significant difference in the incidence of cerebrovascular and cardiovascular events between the two groups, and the results suggested that blood pressure reduction per se did not necessarily lead to a parallel decrease in cerebrovascular and cardiovascular complications. (Hypertens Res 1995; 18: 235-244)