The clinical significance of the pressor response triggered by blood pressure measurement, the so-called “white-coat effect, ” was studied in relation to left ventricular structure and function in patients with essential hypertension. We studied 75 consecutive, never-before treated patients with essential hypertension (54±2 (SE) years; 31 men). Beat-to-beat blood pressure (Finapres) was monitored at rest, during conventional blood pressure measurement by a doctor, and during a mental stress test. The left ventricular mass index and diastolic function (E⁄A ratio) were determined by echocardiography. The systolic blood pressure response triggered by the doctor’s visit (ΔSBP) correlated positively with the left ventricular mass index (r =0.326, p<0.03) and negatively with the E⁄A ratio (r =-0.325, p<0.02). A positive relationship between the ΔSBP and left ventricular mass index was observed in men (r =0.556, p<0.01) but not in women. The greater ΔSBP also was associated with lower E⁄A ratio in women (r =-0.434, p<0.02). The ΔSBP correlated with the mental stress-induced increase in systolic blood pressure in men (r =0.586, p<0.005) but not in women (r =0.148, n.s.). Blood pressures outside the clinic were higher in men than in women (p<0.05 for systolic and p<0.005 for diastolic) despite the similar level of clinic blood pressures between the sexes. Stepwise multiple linear regression analysis showed that the ΔSBP was an independent predictor of the left ventricular mass index in men (β=0.783, p =0.0009) and of the E⁄A ratio in women (β=-0.003, p =0.05). These data suggest that the pressor response triggered by a doctor’s visit has clinical significance in never-before treated hypertensive patients, possibly because it mirrors real-life stress reactivity in men. (Hypertens Res 2002; 25: 343-349)