The rate of incidence of malignant pleural mesothelioma is increasing although diagnosis of this disease may be very difficult. Computed tomography examinations and conventional chest x-rays of 30 patients with malignant pleural mesothelioma were reviewed independently, to evaluate the role of both modalities. CT offered the following advantages over conventional chest x-ray examinations: CT was more sensitive in detecting the smooth and nodular changes of malignant pleural mesothelioma, especially at the diaphragm and lower parts of the thorax, tumours could be better demonstrated at the pericardium and in the greater fissure, in some cases, where chest films showed just abnormal widening of the mediastinum, CT could differentiate between tumour involvement of the mediastinal pleura and local invasion of the mediastinum by the tumour, CT was more effective in detecting pleural calcifications and thickening of the contralateral pleura. CT proves more accurate in assessing the extent of the disease, and gives additional diagnostic help.