The antihypertensive efficacy of a 1.5-mg sustained-release formulation (SR 1.5) of indapamide, a diuretic related to thiazide, has been pointed out by using conventional sphygmomanometric measurement 24 h after dosing in clinic, in two large European randomized, double-blind, controlled studies (2 and 3 months). One of these studies was then extended to 12 months, as a complementary open study. Quality-controlled ambulatory blood pressure monitoring (ABPM) data for a total of 216 patients from these studies are presented, including subgroups of hypertensives and responders. Indapamide SR 1.5 achieves an adequate 24-h blood pressure control by significantly reducing the 24-h, diurnal, and nocturnal blood pressures versus baseline, confirming the sphygmomanometric data. The benefit at 2 and 3 months is maintained at 1 year, which confirms the long-term efficacy of SR 1.5 mg. The trough-to-peak ratio-not previously calculated for a diuretic according to international guidelines-meets Food and Drug Administration requirements and confirms the 24-h efficacy of indapamide SR 1.5.