The ideal therapy for patients with isolated systolic hypertension remains unclear; diuretics, calcium channel blockers, and angiotensin-converting enzyme (ACE) inhibitors are all used in clinical practice. The aim of this study was to determine whether a fixed-dose ACE inhibitor/diuretic combination would reduce ambulatory blood pressures (BP) and arterial stiffness in isolated systolic hypertension more than antihypertensive monotherapy. In this randomized, double-blind study, 8 weeks of fosinopril/hydrochlorothiazide combination (10/12.5 mg titrated up to 20/12.5 mg) was compared with the calcium channel blocker (amlodipine, 5 mg titrated up to 10 mg) and diuretic (indapamide, 2.5 mg) monotherapy in 28 patients with isolated systolic hypertension. Each patient received all 3 therapies. Assessments included 24-hour ambulatory BP, clinic BP, and applanation tonometry-derived augmentation index. At 8 weeks, the fall in average 24-hour systolic BP and night time systolic BP were significantly greater in the fosinopril-hydrochlorothiazide group, compared to amlodipine and indapamide. The decrease in augmentation index and central aortic systolic BP was also greater in the fosinopril-hydrochlorothiazide group, compared to either amlodipine or indapamide. There was no difference between therapies in decrease in clinic systolic or diastolic BP, or diastolic ABP (average 24-h, diurnal, or nocturnal). Compared with either calcium channel blocker or diuretic therapy, a fixed-dose ACE inhibitor-diuretic combination induces greater reductions in systolic ABP, particularly at night, favorable effects that may be related to a decrease in the intensity of or delay in arterial wave reflections. ACE inhibitor-diuretic combination therapy is a useful approach to cardiovascular risk reduction in isolated systolic hypertension.