Forty patients with malignant mesothelioma were studied to assess the efficacy of current treatment concepts and to examine clinical features at diagnosis which correlate with prognosis. Sixty-three per cent had been exposed to asbestos. Women, patients who presented with limited disease and those who had had symptoms for more than six months before diagnosis survived significantly longer (p < 0.02). Patients who presented with dyspnea had a median survival of 14.2 months, twice the survival (7.8 months) of patients whose first complaint was of chest pain (p < 0.32). No prognostic significance could be found for a history of smoking or asbestos exposure, pathologic subtype or pleural versus peritoneal presentation. Thirty of the 40 patients underwent open thoracotomy or laparotomy for diagnosis. The median survival of the 10 patients in whom a subtotal resection was attempted was 15 months, contrasted to 8.5 months for the 24 patients who underwent only an open biopsy. Five patients received aggressive radiotherapy, four immediately following subtotal surgical resection and one after biopsy alone. These patients survived a median of 9.21 months, with one patient disease-free at 52 months after diagnosis. Twenty-nine patients received chemotherapy. A partial response occurred in nine of 22 (40 per cent) previously untreated patients given Adriamycin TM-containing regimens. Patients who received chemotherapy survived a median of 15 months. In contrast, five patients (four who presented with limited disease) who accepted only supportive care survived a median of only 4.2 months after diagnosis. The treatment of mesothelioma is often based on protocols designed for sarcomas. Unlike patients with sarcoma, who generally die of metastatic disease, 78 per cent of our patients who could be evaluated died of complications of their local primary disease. We conclude that mesothelioma is sufficiently different from sarcoma to justify its treatment as a separate disease entity. Otherwise healthy patients with disease limited to a single hemithorax should be offered maximal tumor resection, followed by postoperative radiation therapy to areas of residual disease, followed by chemotherapy with a regimen containing Adriamycin.