Gallbladder cancer is the most common malignant tumor of the biliary tract, but its early diagnosis is uncommon. The use of ultrasonography has increased the detection of benign gallbladder tumors, and the premalignant potential of gallbladder adenomas is now undisputed. Adenomyomatosis of the gallbladder has recently been suggested to have malignant potential, and we report a case of adenocarcinoma of the gallbladder occurring in localized adenomyomatosis that was successfully treated by radical curative surgery. The more rigorous use of ultrasonography and a more aggressive approach to "benign" polypoid lesions of the gallbladder may represent the best way of achieving early diagnosis and cure in gallbladder cancer.