The 4 year prospective trial on the effectiveness of the antihypertensive treatment was performed in 100 mild hypertensive patients of the aged, the average age being 76.1 years. Dropouts during the drug-off control period were 9 cases. The matched pair group was selected by the age, sex, and blood pressure. Forty-four drug treated cases and 47 placebo treated cases were comparable in blood pressure as well as in laboratory data. Cerebrovascular and cardiac complications were observed in 4 cases or 10.5% in the drug group, and in 9 cases or 22.0% in the placebo group. When 8 cases of blood pressure elevation over 200/110 mmHg in the placebo group were added to the cardiovascular complications, dropouts in placebo group reached 41.5%, and this showed the significant difference. Other complications were observed in 12 cases or 31.6% in the drug group and in 17 cases or 41.5% in the placebo group. Major complications were cancers, infections, and bone or joint diseases. Blood pressure was decreased from 171/87 to 151/80 in the drug group, and the average decrease was 20/7 mmHg in 4 year period. No significant changes in hematocrit, serum protein, urea nitrogen, uric acid, sodium, and potassium were observed during the trial period. The present study suggested that antihypertensive treatment was effective in the aged with mild hypertension, and that careful follow up was needed not only for cardiovascular complications but also for general health condition.