F LUORODEOXYGLUCOSE (FDG) is well established as a tumor-seeking agent that is taken up by a wide variety of malignant tumors. Several nonmalignant lesions also are FDG avid, as are normal organ systems that use glucose as part of their metabolism. Low-grade FDG uptake in muscles is part of the normal biodistribution pattern of FDG, especially during physical activity. When this uptake is symmetric and corresponds to the location of a specific group of muscles, it is easily recognizable. Accurate interpretation of asymmetric muscular activity is more difficult. Recognition of unusual patterns and the location of benign physiologic muscular uptake of FDG is important for avoiding misinterpretations of positron emission tomography (PET) images. I describe 4 cases with unusual muscular FDG uptake that was noted during whole-body FDG imaging of nondiabetic patients. CASE 2