Pulmonary alveolar proteinosis is an uncommon disorder marked by the abnormal accumulation of surfactant within the alveoli. Secondary pulmonary alveolar proteinosis develops in patients who are immunosuppressed, usually with corticosteroids. We present a case of biopsy-proven pulmonary alveolar proteinosis in a patient undergoing therapy with the disease-modifying antirheumatoid arthritis drug leflunomide (Arava; Aventis Pharmaceuticals, Bridgewater, NJ). He was treated with whole lung lavage and discontinuation of leflunomide with good results. This is the first reported association of secondary pulmonary alveolar proteinosis with leflunomide therapy. Pulmonary alveolar proteinosis should be considered in patients with diffuse lung disease that develops while on disease-modifying antirheumatoid arthritis drug therapy.