The CT scans, plain films, and clinical courses of nine patients with malignant pleural mesothelioma were reviewed to assess the value of computed tomography (CT) in the initial evaluation and follow-up of this malignancy. The initial pretreatment scans showed a typical lobulated rind of pleural tumor encasing the lung associated with variable amounts of pleural fluid. Local invasion of the mediastinum, pericardium, diaphragm, and contralateral thorax were well depicted on CT; unsuspected abdominal extension of tumor was demonstrated on CT scans of five patients. Serial scans during treatment provided objective evidence of either regression or growth of tumor mass, even when the patients' clinical status and plain films appeared stable.