Diabetic mellitus (DM) has many well-known complications. However, there is one rare complication, diabetic muscle infarction (DMI), which is usually under diagnosed. Hereby, we present a 53-year-old Chinese man with a history of DM, hypertension and atrial fibrillation. He had acute onset of severe left lower leg pain and swelling with difficulty in walking 4 days before admission. Physical examination revealed non-pitting and non-erythematous swelling with cold sensation of the left medial calf muscles. Magnetic resonance image (MRI) showed homogenous high signal changes in the calf muscles on T2 images, which indicated DMI. After anticoagulation treatment, the patient had a fair recovery within 4 weeks and he could walk by himself thereafter. DMI is a rare complication of poorly controlled DM. It does have a characteristic clinical presentation and MRI findings. Increased clinical awareness is important for early recognition and correct treatment.