Diastolic dysfunction is common in hypertrophic cardiomyopathy (HC). Previous studies suggest that Doppler transmitral flow velocity profiles, and the left atrial (LA) M-mode echogram can be used noninvasively to evaluate left ventricular (LV) diastolic function. However, this has not been proved in HC. In this study we determined the relation of Doppler transmitral flow velocity profiles and the LA M-mode echograms to invasive indexes of LV diastolic function in patients with HC. We studied 25 patients with HC, while off drugs, and calculated LA global and active fractional shortening and the slope of both early and late displacement of the posterior aortic wall during LA emptying by M-mode echocardiography. We calculated peak velocity of early (E) and atrial (A) filling, E to A ratio, and E-wave deceleration time by pulsed Doppler echocardiography, and simultaneous radionuclide angiography, LV pressures, time constant of isovolumic relaxation tau, and the constant of chamber stiffness k by cardiac catheterization. The time constant of isovolumic relaxation tau correlated with the slope of early posterior aortic wall displacement (r = 0.59; p <0.01). LV end-diastolic pressure correlated with global LA fractional shortening (r = -0.75; p <0.001); the constant of chamber stiffness k correlated with active LA fractional shortening (r = -0.53; p <0.02). In a subset of 13 patients, in whom echocardiography and cardiac catheterization were performed simultaneously, similar results were found. LA M-mode recordings provide a more reliable noninvasive assessment of diastolic function in HC than mitral Doppler indexes.