Chest radiographs of 43 patients with Rocky Mountain spotted fever were reviewed to elucidate the frequency and types of involvement of the lower respiratory tract. The abnormal radiographic patterns included localized and diffuse infiltrates of both interstitial and alveolar type. Autopsies were performed in five cases, and findings in several of these are described to help provide radiologic-pathologic correlation. An association of lung involvement (as evidenced by diffuse infiltrates on chest radiographs) and increased mortality was demonstrated.