Adenomyomatosis of the gallbladder (AMG) is characterized by mucosal hyperplasia leading to invagination through the thickened muscle layer, which is relatively common in adults, but is rare in childhood. We report a 12-year-old boy with adenomyomatosis of the gallbladder combined segmental and fundal type. This combined type is rare in adults and is first reported here in childhood. Although initial imaging with computed tomography (CT) suggested the presence of a circular solid mass-like lesion because of its rare morphology, repeated ultrasonography (US) was useful for leading to a correct diagnosis.