This report is based on a clinical and pathologic study of fifty-six operatively removed specimens of malignant gallbladders. Microscopic sections were made and stained with hematoxylin and eosin; the corresponding case histories were studied and comparisons were made. The series does not comprise the total number of malignant lesions of the gallbladder removed at the Mayo Clinic, but only those specimens available and suitable for study. The records of the pathologic museum show that 14,978 gallbladders removed at operation were sent to the museum between 1910 and 1927, and that 89 of these were malignant. INCIDENCE The incidence of malignancy of the gallbladder is commonly given as ranging from 0.5 to 5 per cent. Murphy,1 in one of his clinics, stated that carcinoma of the gallbladder is a rare disease. W. J. Mayo,2 in an earlier report on 405 operations performed on the gallbladder and biliary passages for all causes,