A 54-years-old woman suffered from a bilateral pelvic and lumbar pain. She had a systemic investigation shows a diffuse bone lesions. A biopsy of iliac bone was done and revealed sarcoidosis. Bony manifestations of sarcoidosis are rare and challenging to diagnose. Our report shows that MRI with diffusion weighted sequences is a simple and non invasive technique to evaluate bone infiltration. It helps to distinguish inflammatory disease from metastatic lesions and to guide the osseous biopsy. Moreover, fluorodeoxyglucose PET scan, are useful in establishing the extent of damage and measuring disease activity.