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Bone scintigraphy is very sensitive in detecting metastases in an early stage, when changes in osteoblast function precede morphologic changes. In many oncologic situations, however, osteoarticular abnormal changes seen on the bone scan are not caused by tumor infiltration. They may be due to tumor associated conditions, such as carcinoma polyarthritis and hypertrophic pulmonary osteoarthropathy. They also may be due to therapy-associated conditions, such as the flare effect on metastases due to hormonal treatment, chemotherapy or radiotherapy, and osteonecrosis as a complication of radiotherapy or the use of corticosteroids. The introduction of Colony Stimulating Factors (CSF) to reduce myelotoxicity have allowed higher doses of chemotherapeutic agents to be administered. Currently, there is research being performed on the clinical effects of CSF in phase-ll studies. In addition to the flare response of metastases, increased uptake in the axial skeleton and/or juxta-articular areas on bone scintigraphy in five patients receiving CSF has been observed. This new phenomenon could be explained by a reaction to a very cellular marrow caused by the use of CSF. The clinical relevance of this finding remains to be established. The authors present an overview of these old and new phenomena seen on the bone scan with clinical and roentgenologic correlation.