Adenomyomatosis is a hyperplastic disease of gallbladder and its etiology was unknown. There is hyperplasia of the wall with intramural mucosal diverticula formation (Rokitansky-Aschoff sinuses) penetrating into the muscular wall of the gallbladder with or without gallbladder wall thickening. It was usually asymptomatic; unless there wasn't have concomitant biliary disease. In this case report, we are presenting a 48-year-old women patient, who coming to the emergency room because of abdominal pain, nausea and vomiting, who has an acute cholecystitis and gallbladder adenomyomatosis which was confused with gallbladder cancer.