To compare the effects of exercise training and hydrochlorothiazide on left ventricular (LV) geometry and mass, blood pressure (BP) and hyperinsulinemia in older hypertensive adults, we studied 28 patients randomized either to a group (n = 16, age: 66.4 ± 1.3 yrs old) that exercised or to a group (n = 12, age: 65.3 ± 1.2 yrs old) that received hydrochlorothiazide for 6 months. Endurance exercise training induced a 15% increase peak in aerobic power. The reduction in systolic BP was 2-fold greater with thiazide than with exercise (26.6 ± 12.2 mm Hg vs. 11.5 ± 10.9 mm Hg). Exercise and thiazide reduced LV wall thickness, LV mass index (14% in each group) and the LV wall thickness-to-radius (h/r) ratio (exercise, before: 0.48 ± 0.2, after: 0.42 ± 0.01; thiazide, before: 0.47 ± 0.04, after: 0.40 ± 0.04, p = 0.017) similarly. The reductions in systolic BP and the h/r ratio were correlated in the exercise group (r = 0.70, p = 0.005) but not in the thiazide group. Exercise training reduced glucose-stimulated hyperinsulinemia (before: 13.65 ± 2.6 vs. 9.84 ± 1.15 mU/ml X min, p = 0.04) and insulin resistance. Thiazide did not affect plasma insulin levels. The results suggest that while exercise is less effective in reducing systolic BP than thiazide, it can induce regression of LV hypertrophy similar in magnitude to thiazide. Unlike hydrochlorothiazide, exercise training can improve insulin resistance and aerobic capacity in older hypertensive people.