Pulmonary arterial hypertension was found in a patient with myeloma who had a diffuse lung lesion. Echocardiographic and hemodynamic data from pulmonary arterial catheterization demonstrated relatively well-preserved left ventricular function. The diagnosis of diffuse pulmonary amyloidosis was established by open lung biopsy, which revealed severe diffuse vascular deposition of amyloid with mild involvement of the alveolar septa. Pulmonary arterial hypertension secondary to vascular deposition of amyloid in the lungs is rare. This case corroborates the clinicopathologic relationship.