A 45-year-old woman with 20-year history of diabetes mellitus was admitted to our hospital because of high fever and abdominal pain. Radical hysterectomy and bilateral pelvic lymphadenectomy had been performed 4 months before admission for invasive cervical cancer. On admission, elastic hard tumors were palpable in the lower abdomen. Laboratory examination showed positive C-reactive protein (CRP), anemia and renal dysfunction. Computed tomography (CT) revealed several lymphocysts in the pelvis. She was diagnosed with infection of pelvic lymphocysts. Since her mother also had diabetes associated with deafness, we examined mitochondrial DNA in leukocytes and detected an A to G transition at the nucleotide position of 3243 (A3243G mutation). She was diagnosed as maternally inherited diabetes mellitus and deafness (MIDD). Puncture of the cysts followed by administration of antibiotics resulted in marked improvement of symptoms and laboratory findings. This is a rare case of pelvic lymphocyst infection in a patient with a mitochondrial disorder. Although the exact mechanism of infection is not clear, MIDD may represent an unusual risk factor for infection, and further investigation is necessary to assess the influence of mitochondrial dysfunction on the immune system. Pelvic lymphocyst infection should be considered in the differential diagnosis of abdominal pain and fever in patients with MIDD after abdominal surgery.