Diabetic muscle infarction (DMI) is a rare complication of diabetes mellitus. We report the first recorded case in Japan. A 45-year-old Japanese woman presented with severe pain in the left antero-medial thigh. She had a 14-year history of Type 2 diabetes mellitus (DM). She had first noticed pain in her left thigh after a walk 2 weeks prior to presentation. The pain worsened progressively. She noticed a firm mass in her left thigh. T2-weighted magnetic resonance imaging (MRI) demonstrated a high-intensity signal in the muscle bulk of the anterior component of the left thigh. A needle biopsy of the mass showed necrosis. She was treated with bedrest and an antiplatelet agent. The mass disappeared 8 weeks after admission. DMI is a rare complication of poorly controlled diabetes mellitus. Twenty-seven cases with DMI have been reported in the English literature but we believe this is the first Japanese case with DMI.