Thirty-seven untreated subjects with borderline or mild hypertension were studied to establish the prevalence and clinical characteristics associated with abnormal left ventricular filling in this disorder. Subjects were referred to this study because of casual office blood pressure measurements of ≥140/90 mm Hg; all were <50 years old, had no other cardiovascular or systemic disease and had not received antihypertensive medication for at least 1 year. To precisely determine blood pressure, measurements were made over 30 min with the patient in the supine position and during awake hours with ambulatory monitoring. Left ventricular mass was determined echocardiographically, and Doppler echocardiography was used to assess left ventricular filling. No subject had increased left ventricular mass, but 8 (22%) of the 37 had abnormal left ventricular filling. All eight subjects with abnormal left ventricular filling had an ambulatory systolic blood pressure >130 mm Hg and a supine systolic blood pressure >122 mm Hg. Abnormal filling was not related to left ventricular mass or heart rate. In multivariate analysis, the degree of abnormal filling could best be predicted from a combination of age and supine systolic blood pressure (r = 0.69; p < 0.001). This study suggests that in untreated early essential hypertension, abnormal left ventricular filling is present in >20% of subjects, precedes detectable left ventricular hypertrophy and is related to age and prevailing level of blood pressure.