Left ventricular outflow tract (LVOT) obstruction is predictive of a worse outcome in hypertrophic cardiomyopathy (HCM). In a detailed Doppler echocardiographic study of 178 selected HCM patients, the group of patients (n = 73) with the obstructive form (resting peak gradient > or = 30 mmHg) presented more hypertrophy and poorer systolic and diastolic left ventricular (LV) functions than the HCM group (n = 105) without obstruction. LVOT peak gradient was positively correlated with hypertrophy (P < 0.0001) and negatively to tissue Doppler mitral annulus systolic (P = 0.0001) and early diastolic (P < 0.0001) velocities. The gradient significantly correlated with E/Ea ratio (r = 0.67; P < 0.0001). By multiple regression, LVOT gradient was related to E/Ea, LV maximal thickness and left atrial size. In comparison with patients without obstruction, patients with obstruction presented greater hypertrophy (P < 0.0001), lower systolic and early diastolic mitral annulus velocities (both P < 0.0001), higher E/Ea ratio (P < 0.0001) and higher global function index (P < 0.0001). In HCM, beyond the effects on hypertrophy, LVOT obstruction is an independent determinant of LV functional abnormalities.