The objective of the present study was to assess the relationship between microalbuminuria (Malb) and left ventricular hypertrophy (LVH), when levels of ambulatory BP was token in to account as a confounder factor. Patients with essential hypertension, aged 25 to 50 years old, never treated with antihypertensive drugs, were included in the study. The inclusion criteria were: (a) absence of diabetes, renal disease or urinary tract infection; (b) urinary albumin excretion (UAE) estimated in urine of 24 hours in two separate days; (c) echocardiography suitable for measurement of left ventricular mass (LVM); and (d) good quality ambulatory blood pressure monitoring during 24 hours. UAE was measured using a immunonephelometric assay (Behring Institute) and Malb was considered when UAE 30 to 300 mg/24 hours during the two days. LVM was calculated by the Devereaux formula and referred to height (LVMI g/m). AMBP was performed using an oscilometric device (Spacelabs 90202 or 90207) during a regular working day. Readings were programmed every 20 minutes between 6 a.m. to midnight and thereafter every 30 minutes. The average BP during a 24 hour period was calculated. One hundred and fifty one patients (96 male, mean age 37 +/- 8 years, body mass index 27.7 +/- 3.7 g/m2) were included. The average values of office BP was 148 +/- 15/96 +/- 8 mm Hg, and the average BP during 24 hours was 137 +/- 13/88 +/- 12 mm Hg. UAE was 30.1 +/- 52.3 mg/24 hr and the LVMI 140.6 +/- 44.1 g/m. The percentage of Malb patients was 28% and those with LVH 34%. A significant relationship between UAE and office and ambulatory SBP and DBP was observed. LVMI was also significantly related to ambulatory SBP and DBP, a relationship that was not found for office BP. In a multiple regression model, significant relationship between UAE and LVMI emerged, independent of diastolic ambulatory BP, age and sex (P < 0.04). In conclusion; we observed a significant relationship between UAE and LVMI, in part, independent of blood pressure. The fact that Malb is associated with the presence of LVH, supports the idea that Malb is a risk marker in essential hypertensive patients.