Paget's disease is a disorder of aging bone which occurs in the setting of accelarated bone remodelling. In the presented case we discuss the difficulties in the diagnosis of Paget's disease in a 77 year old patient with coexisting endometrium carcinoma. The patient was initially diagnosed with metastatic bone disease due to endometrium adenocarcinoma when she was admitted to oncology clinic with pelvic pain. Bone scintigraphy with Tc99 and (18) F fluorodeoxyglucose positron emission tomography/CT revealed an increased uptake on the bone lesions which were reported as metastatic bone involvement. Although the (18) F-FDG uptake was much higher than the levels that would generally be anticipated in a case with Paget's disease, high levels of bone turnover markers indicated further evaluation in the differential diagnosis and the definitive diagnosis of Paget' s disease was established with the pathological evaluation of bone biopsy.