BACKGROUND We report the CT findings of parenchymal and pleural diseases in a group of patients with a history of asbestos exposure, excluding lung cancer (which is not typical in this subjects) and asbestosis (which is a parenchymal fibrosis). METHODS We retrospectively reviewed a series of CT examinations (conventional, helical and high resolution scans) of 21 patients examined from 1995 to 1999. They had pleural plaques (10), round atelectasis (2) and malignant pleural mesothelioma (9). All patients had a history of direct or indirect asbestos exposure, except one with malignant pleural mesothelioma. We evaluated the following CT findings: nodular, plaque or uniform pleural thickening; pleural calcifications; pleural thickening less or greater than 1 cm; pleural margins (regular, polycyclic, spiculated); localization (uni/bilateral hemithorax); distribution (upper, medium or lower region); pulmonary, mediastinal and diaphragmatic involvement; fissural involvement; pleural effusion; lymph node enlargement; lung mass with the comet-tail sign; lung volume (normal, reduced, increased). RESULTS Pleural plaques were always bilateral and less than 1 cm thick, with calcifications in 80% of the cases. Margins were always regular, polycyclic in 40% of the patients and never irregular. The pulmonary pleura in the mid-chest was involved in cell cases the diaphragmatic pleura in the 50% of the cases and the upper and lower regions in 60% and 80% of the patients, respectively. Round atelectasis (3 cases in 2 patients) was always shown as a parenchymal mass in the lower lobes, posteriorly or posteromedially, with adjacent pleural thickening; its diameter ranged 4.4-6 cm and there was the comet-tail sign. In malignant pleural mesothelioma we always found pleural effusion, with unilateral pleural effusion being the only sign in 2 patients. Other findings were pleural nodules (77.7%), with spiculated (22.2%) and polycyclic (77.7%) margins, more than 1 cm in diameter. The disease was always unilateral. The parenchymal pleural was involved in 77.7% of the cases while the mediastinal and diaphagmatic pleura were involved in 44.4% of the patients. Fissural involvement was demonstrated in 66.6% of the patients. Lymph nodes were enlarged in 66.6% of the cases. The volume of the affected hemithorax was increased (22.2%), decreased (44.4%) or normal (33.3%). CONCLUSIONS The presence of pleural plaques is a specific sign of asbestos exposure. Round atelectasis may also indicate asbestos exposure, but it can be found in many diseases with pleural inflammation, such as tuberculous effusion, trauma, pulmonary infarct, congestive heart failure, coronary artery bypass. The CT patterns of these two diseases are typical and no other finding is necessary to confirm the diagnosis. CT-guided needle biopsy is needed only if the round atelectasis has an atypical appearance on CT images, that is without the comet-tail sign. Malignant pleural mesothelioma is strongly associated with previous occupational exposure and presents typical CT findings only in an advanced stage (irregular and nodular pleural thickening, pleural effusion, mediastinal and pulmonary contraction for tumor encasement, parenchymal and lymph node metastases), but the differential diagnosis with pleural metastatic disease can be difficult. CT plays an important role in tumor assessment but biopsy is necessary for lesion characterization.