This study was designed to compare the cardiac mass and geometry in white coat hypertensive patients and established hypertensive patients through the prospective comparison of office blood pressure, daytime ambulatory blood pressure, and echocardiographically determined left ventricular mass and cardiac geometry in consecutive patients. We studied 143 patients from general practice in an outpatient hypertension unit. The patients had newly diagnosed mild-to-moderate hypertension prior to the institution of pharmacological anti-hypertensive therapy. All patients had a diastolic office blood pressure above 90 mm Hg; 90 had a consistently elevated diastolic blood pressure (established hypertension), whereas 53 had an average daytime ambulatory blood pressure below 90 mm Hg (white coat hypertension). Left ventricular mass index was significantly higher in the group with established hypertension, 102.4 +/- 26.6 g/m2 (mean +/- SD) v 93.6 +/- 23.5 (P = .045). Relative wall thickness was likewise significantly higher, 0.36 +/- 0.07 v 0.33 +/- 0.06 (P = .004). There was no significant difference in left atrial dimension. In a multiple regression model the ambulatory measurements and not the office measurements were statistically significantly associated with the extent of cardiac hypertrophy. Further, 44/53 (83%) of the patients with white coat hypertension had normal left ventricular dimensions, versus only 55/90 (61%) of the patients with established hypertension (P = .033). Thus, white coat hypertensive patients display less cardiac involvement than patients with established hypertension, indicating that they should rather be treated as normotensives than as hypertensives, ie, not with pharmacological antihypertensive therapy.