OBJECTIVE To assess racial differences in cardiac structure and function in patients presenting with previously untreated hypertension. METHODS Untreated black patients with hypertension were compared with untreated white patients matched for age and sex. Both groups had similar body mass indices, blood pressures, and reported duration of hypertension. METHODS Cardiovascular risk factor clinic for outpatients. METHODS 36 men and 22 women with untreated essential hypertension. METHODS Variables of heart structure and function on cross sectional and Doppler echocardiography. RESULTS The black patients had a significantly greater interventricular septal thickness (mean 1.23 (95% confidence interval 1.14 to 1.33) v 1.09 (1.02 to 1.16) cm; P = 0.02) and posterior wall thickness (mean 1.14 (1.07 to 1.22) v 0.96 (0.88 to 1.03) cm; P = 0.001) than the white patients, although left ventricular internal diameter was not significantly different (mean 4.90 (4.68 to 5.12) v 4.82 (4.64 to 5.01) cm; P = 0.59). This resulted in a significantly greater left ventricular mass index (mean 151 (137 to 164) v 120 (107 to 133) g/m2; P = 0.001) and relative wall thickness (mean 0.47 (0.43 to 0.51) v 0.40 (0.37 to 0.42) cm; P = 0.004) in the black patients. Comparison of Doppler measures of left ventricular diastolic function showed a significantly longer isovolumic relaxation time in black patients (mean 107 (98 to 116) v 92 (83 to 101) ms; P = 0.02) compared with white patients, although peak early to atrial filling ratios were similar in both groups (mean 1.14 (0.95 to 1.32) v 1.04 (0.94 to 1.15); P = 0.37). CONCLUSIONS Among previously untreated hypertensive patients, black subjects compared with white subjects have significantly higher left ventricular mass index and relative wall thickness, as well as more impairment of left ventricular function during diastole.