A total of 598 males (aged 30-74 years) who had baseline (1961-1970) chest radiography and baseline blood pressure less than 140/90 mmHg were observed prospectively for 10 years. Subjects were participants of the Normative Aging Study, a longitudinal study on aging initiated in 1961 at the Veterans Administration Outpatient Clinic in Boston, Massachusetts. Blood pressures were taken at five- and 10-year follow-up examinations. Multiple logistic regression analysis indicated that the long diameter of the heart (on posteroanterior film) and the cardiac depth (on lateral film) were statistically significant predictors of subsequent hypertension after controlling for baseline body mass index, systolic pressure, and diastolic pressure. A similar model considering various composite indices of heart size indicated that the heart volume was a statistically significant and independent predictor of hypertension. Thus, increases in heart size may precede and predict the development of sustained hypertension.