During an 18-year period, 501 cases of thoracic complications of amebic abscess of the liver were studied; 175 had inflammatory reactions of thoracic structures (165 with pleural effusions and pneumonitis, ten with pericarditis) and 326 ruptured through the diaphragm (175 into the airways, 106 into the pleural cavity, 5 into the pericardium, 39 into the airways and pleura, and 1 into the pleura and pericardium). The thoracic complication was preceded by a picture suggesting an acute inflammatory process or a chronic wasting disease. Depending on type, the complication itself was signaled by increase or change in character of right upper abdominal or lower thoracic pain, dyspnea, or overt respiratory insufficiency, hemoptysis, and expectoration of necrotic material, sepsis, tamponade, and shock. Chest roentgenograms showed small to massive pleural effusions, basal pneumonitis, and cardiomegaly; serology, liver scans, and induced pneumoperitoneum were diagnostic. Treatment included metronidazole and emetine, drainage of pleural or pericardial contents or promotion of bronchial drainage, and meticulous care of associated respiratory, circulatory, and systemic derangements. Mortality for cases with rupture was 11.4 percent, due mainly to sepsis, shock, respiratory insufficiency, and tamponade. The rest of the patients were discharged in cured or improved condition.