Duplications of the gallbladder may be classified as (a) double (two cystic ducts), (b) bilobed (one cystic duct draining a bifid viscus), and (3) diverticulum (c). These anomalies seldom occur in man, particularly the bilobed and diverticulum types. Boyden (2) in 1926 found 15 examples of duplication of the gallbladder in the world's literature and added 5 of his own. He considered none of these to be diverticula. Gross (3) in 1936 reviewed 148 anomalies of the gallbladder, 9 of which he classified as congenital diverticula. Castro (4) reviewed 68 of 74 cases in the Mayo Clinic files up to 1944 that were suggestive of diverticulum of the gallbladder, and accepted only 3 as cases of congenital diverticulum. Report of Case A 50-year-old white woman, a farmer's wife, was registered at the Mayo Clinic on May 13, 1948, complaining of intolerance to fatty foods and episodes of distress at the right costal margin, relieved by vomiting. Cholecystographic examination showed a normally functioning gallbladder. The clinical diagnosis was cholecystitis. The patient was advised to return for cholecystectomy if medical treatment was unsuccessful and was next seen on Jan. 31, 1956. She had been reasonably free from distress until one week prior to this visit, when she had experienced severe pain in the region of the right costal margin, extending into the right subscapular region. Pain and soreness persisted. No jaundice or light-colored stools were noted. The patient weighed 221 lb. and had minimal tenderness at the right costal margin and a palpable thyroid. Routine examinations of the urine and hemoglobin estimates were negative, as were roentgenologic studies of the thorax, esophagus, stomach, and duodenum. Cholecystographic study revealed a functioning gallbladder which contained stones (Fig. 1). The patient was given a weight-reduction program and advised to return for cholecystectomy. Cholecystectomy was performed by Dr. D. O. Ferris on Dec. 29, 1956. The gallbladder was found to be chronically inflamed and to contain multiple stones. The stomach, duodenum, pancreas, liver, spleen, and large and small intestine were normal. The appendix had been removed. The operative cholangiogram did not show any abnormality. Pathologic examination revealed chronic cholecystitis with slight thickening of the walls of the gallbladder. Multiple (seven) faceted stones, each 0.8 cm. in diameter, were localized to a subserosal sac, 1.8 cm. in diameter, adjacent to the fundus (Fig. 2). The mucosa-lined sac communicated with the major lumen through a fundic ostium 0.1 cm. in diameter. Evidence of cholesterosis was present in the main portion of the gallbladder but not in the sac. Muscularis was demonstrated microscopically in the wall of both the gallbladder and the diverticulum. Rokitansky sinuses were also seen in both locations.