Seventeen patients with malignant pericardial effusion were treated by the creation of a pericardial window. This was done through a subxiphoid approach in 13 patients and through limited anterior thoracotomy or sternotomy incisions in 4. There were no deaths and no major complications attributable to the operation. In all patients, relief of the cardiac compression caused by the effusion was immediate and complete. No patient showed a clinically significant recurrence of the effusion, although 1 patient who had received irradiation required pericardiectomy for constriction 5 months later. Survival was determined principally by the extent of the primary malignancy. Six patients died of the primary tumors within 30 days, but 6 survived 3 to 12 months and 2 are alive at 8 and 21 months. It is concluded that creation of a pericardial window, preferably by the subxiphoid approach, is the treatment of choice for malignant pericardial effusion. The procedure provides an accurate diagnosis, carries virtually no mortality or morbidity, and affords immediate and long-lasting relief of cardiac compression.