The authors report two cases of apparent adult respiratory distress syndrome (ARDS) following limited thoracic irradiation for lung cancer. Respiratory failure followed rapidly after irradiation with diffuse bilateral infiltrates, both in and out of the irradiated volume along with progressive hypoxemia unresponsive to oxygen management. Other potential causes of lung injury such as lymphangitic tumor, cardiac failure, and infections were excluded by both premortem and postmortem examination. Autopsy findings in both irradiated and unirradiated volumes of lung were consistent with hyaline membrane changes. The possible relationship between radiation therapy to limited lung volumes and the development of adult respiratory distress syndrome is discussed.