Early identification of left ventricular (LV) structural changes may have an impact on the outlook of patients with essential hypertension. Of 669 untreated hypertensive subjects, 496 (74%) with normal LV mass at echocardiography (< 125 g/m2) were grouped according to normal LV geometry (n = 303; 61%), asymmetric LV remodeling due to isolated septal thickening (n = 111; 22%), asymmetric LV remodeling due to isolated posterior wall thickening (n = 5; 1%), or concentric LV remodeling due to septal and posterior wall thickening (n = 77; 16%). Remodeling was defined as twice the thickness of septum or posterior wall divided by the internal diameter at end diastole > 0.45. Twenty-four-hour noninvasive ambulatory blood pressure (BP) monitoring was performed in all subjects. Compared with subjects with normal LV geometry, those with asymmetric LV remodeling due to isolated septal thickening showed increased clinic BP (158/100 vs 153/97 mm Hg, both p < 0.05), mean daytime ambulatory BP (144/95 vs 138/90 mm Hg, both p < 0.01), mean nighttime ambulatory BP (128/80 vs 122/76 mm Hg, both p < 0.01), LV mass (99 vs 89 g/m2, p < 0.001), total peripheral resistance (1,881 vs 1,562 dynes s cm-5, p < 0.01) and known duration of hypertension (5.5 vs 3.6 years, p < 0.01) and decreased stroke index (39 vs 47 ml/m2, p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)