Metastatic bone disease is the most common malignancy of bone, and is the source of significant morbidity in cancer population.Bone scintigraphy remains the most frequently performed nuclear medicine study and the most cost-effective and available whole-body screening test for the assessment of bone metastases in spite of its low sensitivity for detecting early marrow lesions and purely lytic lesions.Positron emission tomography (PET) is the gold standard in metabolic imaging and is characterized by high-contrast resolution, whole body tomographic data and the ability to perform absolute quantitation of tracer uptake. PET may be superior to bone scintigraphy in the detection of metastases because it detects the presence of tumor directly by its increased metabolic activity, rather than indirectly by showing tumor involvement due to increased bone mineral turnover. This has allowed the detection of metastatic marrow lesions earlier than with bone scintigraphy, & is sometimes more accurate in evaluation of the therapeutic response of bone metastases.