Nuclear medicine plays an important role in staging and evaluation of the initial extension and response to treatment of bone metastases. In order to accurately read Bone Scintigraphy (BS) and Positron Emission Tomography scan (PET) procedures, it is essential to understand the different behavior of these studies. We present a case report of a woman treated for breast cancer, with suspicion of recurrent disease due to increase of tumor markers. Initial BS showed non-conclusive findings, whereas PET study was consistent with a spread of bone metastases. The patient underwent both procedures again after a course of chemotherapy. Post-treatment BS showed progression of bone lesions, while PET showed good therapeutic response. The PET demonstrates lesions earlier and more effectively than the bone scintigraphy in the evaluation of the therapeutic response of bone metastases.