Between 1969 and 1992, eighty cases of malignant pericarditis were studied by thoracotomy and biopsy, which made it possible not only to assert the diagnosis but also to dry the pericardial effusion by creating a pleuro-pericardial window. In 75 cases a cardiac tamponade of varying severity required surgical heart decompression. Pericarditis revealed the neoplasia in 53 cases and complicated a known cancer in 27 cases (23 carcinomas, 2 malignant melanomas included). In 63 cases (2 metastatic malignant melanomas, 7 sarcomas and 54 carcinomas) the disease was rapidly fatal. On the other hand, 17 patients with certain types of neoplasia revealed by pericarditis (12 with malignant lymphoma, 5 with non-encapsulated thymoma) have survived under an appropriate treatment. In addition to curing the immediately life-threatening tamponade, thoracotomy with pericardial biopsy determines the nature of the lesion and, consequently, its specific treatment.