BACKGROUND The 2003 European Society of Hypertension/European Society of Cardiology (ESH/ESC) guidelines recommend angiotensin II receptor antagonists (AIIRAs) as a first-line therapy in hypertensives with left ventricular hypertrophy (LVH). OBJECTIVE We investigated the long-term effects of an AIIRA-based therapy on left ventricular (LV) structure and geometry in previously, unsatisfactorily treated essential hypertensive patients. METHODS Sixty-eight consecutive patients referred to our hypertension hospital outpatient clinic with: (i) LVH (LV mass index, LVMI 51 g/m(2.7) in men and 47 g/m(2.7) in women), (ii) uncontrolled clinic blood pressure (BP140 and/or 90 mmHg) and (iii) antihypertensive therapy not including angiotensin-converting enzyme (ACE) inhibitors or AIIRAs were selected for this study. Two-dimensionally guided M-mode echocardiograms were carried out at baseline and after 6, 12, 18 and 24 months of follow-up. In all patients, losartan (50-100 mg/day, mean dose 82 mg/day) was added as first step to the previous therapy. Additional drugs, tailored to the single patient, were added, if necessary, to achieve target BP values (<140/90 mmHg). RESULTS Overall, 59 patients completed the study with the primary efficacy measurements (LVMI) at all appropriate times. A significant reduction in both clinic systolic BP and diastolic BP was found across the entire period of study respect to baseline (-17/10, -22/12, -24/13 and -26/14 mmHg at 6, 12, 18 and 24 months, p < 0.001 respectively), leading to target clinic BP in 75.6% of cases. LVMI was significantly lower after 1 year of treatment (-11 +/- 12%, p < 0.05) with a further significant reduction at the end of treatment (-22 +/- 18%, p < 0.01). The proportion of patients achieving normalization of LVMI was 47.4% and more importantly, the prevalence of concentric LVH fell from 38.9% to 6.7% (p < 0.01). CONCLUSIONS Our findings indicate that long-term intensive treatment based on the AIIRA losartan induced a normalization of LVH in about 50% of patients and more importantly caused an almost complete regression of concentric LVH, the most dangerous adaptive pattern. The transition from concentric to normal or eccentric LV geometry may have in these high-risk patients a favourable prognostic implication in addition to the recognized positive effect of reducing LVMI.