The clinical course of chronic diffuse interstitial lung disease (ILD) was studied in 14 patients with SLE. The mean duration of follow-up was 7.3 years. All patients had dyspnea on exertion, pleuritic chest pain, chronic cough, and basilar rales. Chest roentgenogram showed diffuse or basilar infiltrates, pleural disease, and elevation of both diaphragms. Systemic corticosteroids were given early in the course of the illness for lung involvement and multisystem disease. Diffusing capacity for carbon monoxide (DLCO) and inspiratory vital capacity (IVC) improved or remained unchanged in the majority of patients. Respiratory complaints improved in all patients; however, two patients died of pulmonary fibrosis and another died of bacterial pneumonia. Alveolar septal deposits of immunoglobulins and complement were found. This study showed that while variability existed among individual subjects, the clinical progression of ILD was slow and tended to improve or stabilize with time.