We report on an uncommon case of diffuse type of adenomyomatosis of the gallbladder. It was initially suspected by ultrasonography and further confirmed by computed tomography (CT) and pathological examination. The patient received a cholecystectomy. The pathologic report showed specific changes of adenomyomatosis corresponding to the finding on the CT scan. No evidence of malignancy is found in the diffuse type of adenomyomatosis of the gallbladder. Although only segmental type of adenomyomatosis of gallbladder has been reported to be related to gallbladder carcinoma recently, the other two types (diffuse & fundal) with cholecystectomy should be checked and followed up carefully.