We report a rare case of hypothermia with acute renal failure in a patient suffering from diabetic nephropathy. A 71-year-old male who had been receiving insulin therapy for the treatment of diabetes mellitus complicated with advanced diabetic nephropathy since 1998 was malnourished with an extremely decreased muscle mass. Without any prolonged exposure to excessively low external temperatures or hypothyroidism, pituitary insufficiency, adrenal insufficiency, sepsis, hypoglycemia, and diabetic ketoacidosis, acute hypothermia appeared together with an aggravation of diabetic nephropathy. His skin temperature fell to below measurable levels and his rectal temperature fell to 30.0 degrees C. His consciousness was drowsy and the hypothermia was not accompanied by shivering. Skeletal muscle is known to play an important role as a center of heat production and shivering thermogenesis in skeletal muscle mainly operates on acute cold stress. Therefore, in this case, hypothermia may have occurred because the shivering thermogenesis could not fully act on the acute cold stress due to the dramatically reduced muscle mass. We should always keep in mind that older, malnourished diabetic patients can easily suffer from impairments of the thermoregulatory system.