Giant cell tumor is a rare complication of Paget’s disease of bone. Typically, this tumor occurs in the case of polyostotic disease and only in pagetic bones. This tumor rarely has been seen in multiple family members who have Paget’s disease, although Paget’s bone disease clearly has a hereditary component. Our report documents four cases of polyostotic Paget’s bone disease complicated by benign giant cell tumor. In two patients, the giant cell tumor also was multifocal. All patients were from one family. They were born in Avellino and reside in Campania, a Southern Italian region. The ancestors of the patients with familial giant cell tumor in Paget’s bone disease were born in the same geographic area. These data suggest that a combination of environmental and genetic factors could be responsible for linkage of the patients born in Avellino with this neoplasm that is highly unusual in patients with Paget’s disease of bone.