We investigated the effect of long-term treatment with a calcium antagonist (nicardipine hydrochloride retard tablet) and a diuretic (trichlormethiazide) on quality of life (QOL) in elderly hypertensives in a multicenter, randomized, double-blind, comparative study (National Intervention Cooperative Study in Elderly Hypertensives Study Group). The percentage of patients who experienced side effects was 17.2% in the nicardipine group and 18.1% in the trichlormethiazide group and 2.9% and 4.3% of participants, respectively, withdrew due to those side effects. These results suggested that nicardipine was tolerated slightly better than trichlormethiazide. There were no significant differences between the two groups in terms of total QOL score or in degree of change (Δ score) before and after calcium antagonist or diuretic administration. Lower score was seen in 3 categories (general symptoms, sleep scale, and sexual function) in the trichlormethiazide group (p<0.05) and in one category (cognitive function) in the nicardipine group, but there was no significant difference in Δ score in any of the individual items. In conclusion, the two antihypertensive agents had nearly equivalent effects on QOL in the long-term treatment of hypertension in the elderly and that neither resulted in a deterioration in QOL. (Hypertens Res 2000; 23: 33-37)