Left ventricular hypertrophy in hypertensives is an important determinant of prognosis. In the present study 45 patients with treated essential hypertension were divided into two groups: 23 patients had normal left ventricular dimension and 22 patients had echocardiographic signs of left ventricular hypertrophy (LVH). All patients were adequately treated during daytime, but ambulatory blood pressure monitoring showed a distinct abnormal pattern in the LVH group characterized by a lack of blood pressure reduction during the night; 16 of 22 patients with LVH had no blood pressure decline during the night, whereas 17 of 23 patients without hypertrophy showed this reduction (P less than 0.01). In conclusion, patients with hypertension and LVH often reveal a lack of blood pressure decline during the night, which may be the reason for the development of left ventricular hypertrophy (and thus should be managed by a different circadian blood pressure therapy) or which may be the consequence of progressive structural changes in the resistance vessels, along with the development of left ventricular hypertrophy. It is suggested that patients with hypertension and left ventricular hypertrophy should have ambulatory twenty-four hour blood pressure monitoring.