A previously healthy 32-year-old man was admitted to the hospital after one month of progressive dyspnea. Although he was hypoxemic, his chest radiograph and spirometry results were normal. His ventilation scan was normal, but a perfusion lung scan revealed bilateral lobar and segmental defects. A venogram of the right leg showed extensive thrombosis of the deep leg veins. After treatment with anticoagulants, the patient progressively returned to normal, and he has resumed his previous, active lifestyle. This patient, who had no apparent risk factors for the development of venous thrombosis and pulmonary embolism, represents a patient population that is generally considered to be at very low risk for this disorder. The presence of a normal chest radiograph and normal spirometry results in a dyspneic patient should prompt a careful evaluation for pulmonary embolism.