Diffuse alveolar hemorrhage is a life-threatening complication after bone marrow transplantation. We investigated the radiographic abnormalities that occurred in 39 transplantation patients with a diagnosis of diffuse alveolar hemorrhage and correlated the findings with the patients' clinical course. The initial radiographic abnormalities after diffuse alveolar hemorrhage developed an average of 11 days after bone marrow transplantation, and the radiographic abnormalities preceded the clinical diagnosis by an average of 3 days. Twenty-seven patients initially had bilateral radiographic abnormalities; 10 initially had unilateral abnormalities (seven in the right lung, three in the left lung). Two patients had normal chest radiographs throughout their clinical course. All 37 patients with radiographic abnormalities had abnormalities involving the central portion of the lung, primarily the middle and lower lung zones. The initial radiographic pattern was interstitial in 27 and alveolar in 10. In 24 patients, radiographic abnormalities were initially judged to be mild; three were severe from the onset. Radiographic abnormalities rapidly worsened in most patients over 6 days. In 30 patients, diffuse bilateral radiographic abnormalities involving all lung zones developed. Eleven patients persisted in having only interstitial radiographic abnormalities; 26 had a confluent alveolar pattern. At the height of radiographic abnormalities, 27 cases were judged to be severe, and only one case was judged to be mild. The mortality rate in patients with diffuse alveolar hemorrhage was 77%. The radiographic abnormalities of diffuse alveolar hemorrhage are nonspecific and usually precede the clinical diagnosis. The clinical course after hemorrhage is short, often resulting in death.