Increased QT dispersion is associated with sudden cardiac death in congestive heart failure, hypertrophic cardiomyopathy, and following acute myocardial infarction. Patients with hypertension, in particular those with left ventricular hypertrophy, are also at greater risk of sudden cardiac death. We examined whether QT dispersion, which is easily obtained from a routine ECG, correlates with echo LVH. Sixty-nine untreated patients with essential hypertension had QT dispersion measured from a surface 12-lead electrocardiogram, and two-dimensional echocardiography performed to measure interventricular septal thickness, posterior wall thickness, and left ventricular internal diameter. Office blood pressure was recorded, and in 56 patients, 24 h ambulatory blood pressure monitoring was also done. Multivariate analysis demonstrated significant relationships between QT dispersion and office systolic blood pressure, and left ventricular mass index. Similar findings were obtained when QT dispersion was corrected for heart rate (QTc dispersion). After patients with electrocardiographic left ventricular hypertrophy (n = 5) were excluded from the analysis, the above relationships persisted. Increased QT dispersion is thus found in those essential hypertensives at greatest risk of sudden death. Since this relationship persists even in the absence of electrocardiographic left ventricular hypertrophy, measurement of QT dispersion might be a simple, non-invasive screening procedure to identify those hypertensives at greatest risk of sudden death.