We report an elderly patient with maternally inherited diabetes with deafness (MIDD). A 69-year-old woman was found to be diabetic for the first time when she visited her local medical doctor for the symptoms of a common cold. Her casual plasma glucose level was 311 mg/dl and HbA1c was 8.3%. She had been aware of muscle atrophy of the lower extremities and hearing disturbance since age 66. As for her family history, her mother, older sister and younger brother were diabetic with hearing difficulty and all of them had died suddenly in their middle age. Her 45-year-old daughter was also diabetic with some difficulty in hearing. Therefore, we suspected both the patient and her daughter had MIDD, and found alterations in mitochondrial DNA3243A-G. MIDD is a condition that needs to be diagnosed accurately and treated at an early stage, since diabetic complications can progress rapidly and could cause myocardial complications and mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS). According to a report of 115 cases of MIDD in Japan, MIDD had been diagnosed at the age of 32.8 on average and our case was strikingly old for the age of onset of the disease.