Right ventricular wall thickness (T) measurements were made in 111 patients by echocardiography to evaluate their usefulness in diagnossing right ventricular hypertrophy (RVH) and in predicting right ventricular peak systolic pressure (P). Anatomic and echocardiographic findings of RVH were compared in 36 of 111 subjects: diastolic T (dT) and systolic T (sT) had a sensitivity of 90 and 34% and a specificity of 94 and 100%, respectively, in the diagnosis of RVH. Echocardiographic and hemodynamic findings were compared in the remaining 75 of 111 patients undergoing cardiac catheterization: dt was 6.5 +/- 2.7 mm in 46 patients with elevated P (58.2 +/- 30.2 mm Hg) versus 3.8 +/- 0.9 in 29 patients with normal P (26.3 +/- 2.7 mm Hg) (p less than 0.01). The dT and P had a linear correlation (r = 0.92) in 40 patients with right ventricular end-diastolic dimension less than 13 mm/m2. Estimates of P in 22 patients with atrial septal defect and right ventricular end-diastolic dimension greater than 13 mm/m2 were fairly good (r = 0.83). It is concluded that echocardiographic measurements of T are useful in diagnosing RVH and in estimating P.