A case of rapid demise following an undiagnosed stercoral perforation is reported. A 57-year-old woman on chronic opioid replacement therapy presented with constipation and abdominal pain to the hospital. Following an unremarkable abdominal radiograph and admission for laxation and pain therapy, she was found dead only 18 h later. To exclude medical malpractice, a postmortem investigation was ordered. Postmortem computed tomography and autopsy revealed fatal fecal peritonitis based on a stercoral perforation of the rectosigmoid, which had been undiagnosed. This report highlights the need for early cross-sectional imaging and contributes to the data collection concerning this ever-growing, vulnerable group of patients undergoing opioid replacement.