We reviewed chest roentgenograms from 17 persons with confirmed Legionnaires' disease. None of the cases was associated with known outbreaks. Pulmonary infiltrates, usually extensive, were present in all cases. The predominant radiological pattern of both on initial roentgenograms and those from the peak of illness was distal air space disease, usually in a segmental or lobar distribution. The lower lobes were involved most frequently. Pleural effusion and volume loss were infrequent. Radiological findings progressed rapidly and often cleared rapidly, although slow clearing was also seen in some cases. Legionnaires' disease should be included in the radiological differential diagnosis of segmental or lobar pneumonia.