The pathological findings in the lungs and related organs of 26 patients (21 female, 5 male) with systemic lupus erythematosus (SLE), with onset of disease before age 20 years, were reviewed. Several categories of lung lesions were found. Chronic interstitial pneumonitis was present in all 26 patients and was severe in 5. Acute pneumonia was present in 20, mild in 13, moderate in 2, and severe in 5. Alveolar hemorrhage, massive enough to cause death in 5, was seen in 18 patients, and pulmonary edema was found in 13. Fourteen patients had hyaline membranes indicative of acute alveolar damage (DAD), 12 had alveolitis obliterans, indicative of prior episodes of DAD, and 9 had bronchiolitis obliterans. Other parenchymal lesions were mild interstitial fibrosis in 12, alveolar hemosiderosis and alveolar overinflation in 10 each, and alveolar septal calcinosis with chronic renal insufficiency in 3. Pleural effusion, pleuritis, or pleural thickening were noted in 15 of 26, 6 of 23, and 7 of 23 evaluable patients, respectively. Vascular lesions were present in 16 as intimal thickening (9), thromboemboli (8), medial hypertrophy (6), calcinosis (3), and vasculitis (2). A previously unreported lesion was chronic (proliferative) peribronchitis, noted in 11 patients. Diaphragmatic lesions included mild variation in fiber size in 7, mild fibrosis in 2, and calcinosis in 1 of 13 evaluable patients. Correlation of the above lesions with previously described lung syndromes in SLE such as lupus pneumonitis, hemorrhagic lung disease, chronic interstitial fibrosis, lupus cor pulmonale, pleurisy, and "shrinking lung syndrome" are discussed.