In this article, we retrospectively review 29 cases of Hamman-Rich syndrome. As in some other recent reports, we have used the term "acute interstitial pneumonia" to emphasize the clinical and pathologic features of these cases and to distinguish them from the more common chronic interstitial pneumonias, particularly idiopathic pulmonary fibrosis. Of the 29 patients, 12 survived, some after a long and complicated hospitalization. The histologic features were those of organizing diffuse alveolar damage, and some patients, including survivors, had extensive fibroblastic distortion of lung parenchyma. The overall survival among these patients was not appreciably different from the survival of patients with the adult respiratory distress syndrome in general.