During the ten year period following Jan. 1, 1930 there were 2,273 patients operated on for nonmalignant extrahepatic disease of the biliary tract in the Massachusetts General Hospital, exclusive of the Phillips House private ward. Of this number, 415 patients, or 18.25 per cent of the whole, had acute cholecystitis. We selected the cases of these patients for study after a careful review of all the records. In every case the diagnosis was supported not only by the operator's opinion but by the pathologic report. All patients had symptoms of acute disease. In 85 per cent pain, tenderness, spasm, palpable mass, a temperature above 101 F. and a leukocyte count above 12,000 were present; with respect to the other 15 per cent, one or another of these findings was not recorded. The most common omission was the presence of a mass in the upper right quadrant of the abdomen. In