An 81-year-old female presented with symptoms of fever, dysuria, back pain, and hyperglycemia. After admission, she had an acute onset of diffuse abdominal pain with rebound tenderness. The CXR revealed pneumoperitoneum. Under the impression of a peptic ulcer perforation, an emergent exploratory laparotomy was performed. Instead a perforated pyometra was found. Although uterine disease is a rare cause of an acute abdomen and pneumoperitoneum in the elderly, a perforated pyometra should be considered in the differential diagnosis.