Clinical and autopsy findings of 2 cases with mixed connective tissue disease (MCTD) associated with severe pulmonary hypertension are reported. Both cases showed marked intimal and medial thickening in small and medium sized pulmonary arteries. In one of the cases plexiform lesions, endarteritis obliterans, and fibrous intimal thickening of the pulmonary veins were recognized. In some cases with MCTD, pulmonary hypertension develops due to pulmonary vascular lesions which are similar to those of primary pulmonary hypertension.