Thirty-six children and adolescents with early stages of idiopathic scoliosis underwent evaluation by echocardiography and pulmonary function testing. Mildly increased pulmonary vascular resistance was inferred from an elevated ratio of right preejection period to right ventricular ejection time, an increased right ventricular dimension, and a decreased left ventricular dimension. Since neither decreased arterial oxygen saturation nor increased end-tidal expired carbon dioxide partial pressure was seen, desaturation and hypoventilation should not account for these abnormalities. Pulmonary function parameters showed no distinct patterns of abnormality. Even though the patients were divided into two groups by severity of spinal curvature, the cardiopulmonary measures did not correlate with thoracic deformity. Billowing of the mitral leaflets, termed mitral valve prolapse, was demonstrated in 25% of the subjects. Our findings suggest that cardiopulmonary and thoracic changes in idiopathic scoliosis may develop in parallel and may be expressions of a common collagen defect. However, study of sleep and exercise arterial saturation may be required to rule out intermittent hypoxemia as a precipitating factor of cor pulmonale in scoliosis.