A 29-year-old female with type I diabetes mellitus developed pain, focal tenderness, and swelling in the posterior left thigh. Subsequent evaluation included a muscle biopsy, which revealed large confluent areas of necrosis and edema, compatible with a diagnosis of diabetic muscle infarction (DMI). Diabetic muscle infarction (DMI) is an unusual neuromuscular complication of diabetes mellitus. DMI begins with the acute onset of focal pain and swelling in the thigh. The anterior compartment (quadriceps muscle group) or posterior compartment (hamstring muscle group) are most frequently involved. The focal region of muscle damage can be noninvasively viewed by magnetic resonance imaging and radionuclide scans. Muscle biopsy demonstrates large confluent regions of muscle necrosis and edema. DMI needs to be differentiated from other processes that can cause leg pain in a diabetic patient.