Lung is the most involved site by infective manifestations in immunodepressed patients. In these patients the variability of pathogenic and opportunistic agents is expressed in the lungs with interstitial and alveolar changes, which are not pathognomonic. CT is the appropriate method to study lung parenchyma. CT by means of fast scans and high resolution algorithms (HRCT) allows an accurated and detailed reppresentation of the lung parenchyma, detecting the secondary lobe, the anatomic and functional unit of the lung and its pathological changes. Our study aim to show the clinical-radiological correlation among the various types pulmonary infections in immunocompromised host.