A thirty-year-old woman had complaints of general fatigue and gain in body weight, which had developed since the third trimester of pregnancy. On admission, she had lip cyanosis, general edema, and tachycardia. A chest rentogenogram showed cardiomegaly and dilatation of the pulmonary arteries. On cardiac catheterization, pulmonary artery pressure and pulmonary vascular resistance were elevated moderately. A pulmonary perfusion scintigram revealed a defect in the left lower lung field with no evidence of thrombus in a pulmonary artery angiogram. In this case, an underlying disease which caused pulmonary hypertension might have been the underfined cause. For this reason, primary pulmonary hypertension was the diagnosis. In the present case there is a danger that congestive heart failure may be induced by pregnancy and delivery and, furthermore, there is a possibility that during the clinical course of the illness pulmonary infarction might occur.