Thirty-five obese (Body Mass Index: BMI > 30) hypertensive (diastolic blood pressure > 100 mmHg) patients were studied for 6 months. 18 patients (10 males, mean age 52 +/- 6 years) were treated with captopril 50 mg b.i.d. (Group 1); 17 patients, matched by age, sex and BMI were treated with captopril 50 mg b.i.d. and hypocaloric diet (Group 2). During follow-up a good control of blood pressure levels (< 150/90 mmHg) and a significant reduction in body weight (> 10%) were achieved in all patients of Group 2. Left heart anatomy was accessed by 2D guided M-mode echocardiogram before starting treatment and after 6 months. In Group 1 Interventricular Septal Thickness (ST), Posterior Wall Thickness (PWT) and Left Ventricular Mass (LVM) decreased significantly (p < 0.01). In Group 2 not only ST, PWT and LVM decreased significantly (p < 0.01 for ST and PWT, p < 0.001 for LVM), but also left atrial dimension (p < 0.05) and left ventricular diastolic dimension (p < 0.01). The percent reduction in AD, LVDD and LVM was significantly higher (p < 0.01) in Group 2. In obese hypertensives relevant weight loss can improve the effect of captopril treatment on left ventricular hypertrophy; the decrease of AD and LVDD is probably secondary to a reduction of the volume overload present in obese patients.