A woman in her 80s who had difficulty walking due to back pain was admitted to our hospital. Until two months earlier, she had been able to live independently in daily life. She was not severely constipated, did not take laxatives, and had not received an enema or undergone stool extraction. She had no abdominal symptoms, such as abdominal pain or distension. Surprisingly, however, computed tomography showed lower rectal perforation with subcutaneous emphysema in the pelvic retroperitoneum, hip, and left inguinal region. Therefore, we urgently performed abdominoperineal resection to save her. The lower rectum is a relatively uncommon site of perforation in the large intestine, and nontraumatic cases are rare. Elderly patients in particular may have only atypical symptoms and thus require careful attention.