Thirty five computed tomography (CT) scans of the thorax and upper abdomen of thirty three patients with malignant pleural mesothelioma were correlated with the findings at thoracotomy (28 patients), thoracoscopy (2 patients) or autopsy (5 patients). Pleural thickening with contrast medium enhancement was detected on the CT scans of all patients. This finding was a valuable diagnostic tool, especially in cases of large amounts of pleural effusion and/or only thin layers of tumour barely or not at all visible on plain film chest X-rays. Difficulties in defining the exact extent of the diseases for clinical staging and/or evaluation of treatment response arose at the following sites: diaphragmatic pleura, chest wall, pericardium, mediastinum and mediastinal lymph nodes. Extension into the lung was difficult to identify following chemo- and/or radiotherapy. Our results show that CT is essential in the clinical management of mesothelioma. We recommend that CT scans of the chest and upper abdomen, using contrast medium enhancement, should be required in routine practice and in particular in clinical trials involving pleural mesothelioma.