Serial chest radiographs from 34 confirmed cases of legionnaire disease diagnosed between February 1979 and June 1981 were reviewed. Initial involvement was most often a peripheral patchy alveolar infiltrate (76%, 26/34) with progression to consolidative pneumonia in 70% (18/26) of these cases. Initial or eventual involvement of noncontiguous lobes (50%, 17/34) was common. Bilateral changes developed in 50% of cases and bilateral diffuse disease developed in 12%. Pleural effusions attributable to legionnaire disease occurred in 32% of the patients. Definite clearing took longer than 2 weeks in 50% of treated patients. The severity of radiographic abnormality correlated with the presence of Legionella pneumophila detectable in sputum by direct immunofluorescence (p less than 0.001). No correlation of radiographic severity to smoking, immunosuppression, advanced age, race, or underlying disease, nor to symptoms of abdominal pain, diarrhea, neurologic abnormalities or high fever, nor to laboratory data including hyponatremia, leukocytosis, or hematuria was found. A comparative review of the literature is provided.