BACKGROUND Having acknowledge the need to treat arterial Hypertension concomitantly effective, safe and easy to comply with. These issues are the mainstay for a good adherence to a treatment that is long. OBJECTIVE This clinical trial addresses the efficacy and safety of an extended release tablet of 180 mg of diltiazem, once daily, to treat mild to moderate hypertension. METHODS Forty-five patients with mild to moderate hypertension were included in a multicentric, open trial consisting of three periods: washout (one week), placebo (one week) and a treatment period of four weeks with 180 mg slow-release tablets of diltiazem. Arterial Blood Pressure (BP) was measured through ambulatory blood pressure monitoring (ABPM) at the end of the first, second and sixth weeks. The therapeutic response was evaluated in terms of decrease in mmHg and in terms of systolic and diastolic loads. Treatment was considered successful when there was a drop in the medium diastolic BP to 90 mmHg or less and/or a decrease of at least 10 mmHg. RESULTS Twenty-three patients completed the trial. There was a significant decrease (p < 0.0001) in the medium diastolic and systolic 24-hour BP values. The efficacy parameters were met in 62.5% of the patients, nonetheless there was a drop of at least 5 mmHg in 82.6%. There was a statistically more significant response during the diurnal versus the nocturnal periods, according to both criteria. CONCLUSIONS Diltiazem, 180 mg extended-release tablet taken one daily, proved to be effective, over 24 hours, in controlling Hypertension in 62.5% of the enrolled patients while decreasing the medium diastolic BP by at least 5 mmHg in 82.5%.