Pyometra, pus within the uterine cavity due to cervical obstruction, is uncommon in postmenopausal women, and spontaneous uterine rupture from pyometra is exceedingly rare but may cause severe peritonitis and sepsis; we report a 57-year-old postmenopausal woman who presented with foul vaginal discharge, progressive lower abdominal pain, fever, hypotension, and ultrasound evidence of turbid intraperitoneal fluid, whose contrast CT demonstrated an endometrial fluid collection with a defect in the posterior uterine wall communicating with the peritoneal cavity; despite initial resuscitation and broad-spectrum antibiotics she deteriorated and underwent urgent exploratory laparotomy, which revealed ~1500 mL of purulent ascites and a 3.0-cm posterior uterine wall perforation, she had a total abdominal hysterectomy with bilateral salpingo-oophorectomy and thorough peritoneal lavage, histopathology confirmed necrotizing endometritis/pyometra without malignancy, and her postoperative recovery was uncomplicated with discharge on postoperative day 9; this case highlights the diagnostic challenge of ruptured pyometra, the value of CT when rupture is suspected, and the necessity of early surgical source control combined with antibiotics to improve outcomes.