The patient, a 33-year-old female, presented to her local doctor with lower abdominal pain. She was referred to our hospital for a plain CT scan, which revealed signs of ileitis. Because acute appendicitis could not be ruled out, the patient was hospitalized. On the third day of hospitalization, she underwent laparoscopic appendicectomy for perforated appendicitis. However, the inflammatory response persisted despite continued antibacterial treatment; we diagnosed this to be due to the formation of a postoperative residual abscess. Since drainage of the abscess was deemed necessary, the patient underwent EUS-guided transrectal drainage on the 26th day of hospitalization. The patient had a favorable postoperative course and was discharged on the 31st day of hospitalization. Along with some literature review, this report details a case in which transrectal drainage under ultrasound endoscopy was effective in treating a pelvic abscess. We report a case of a pelvic abscess that was drained through the rectum under EUS guidance and an internal and external fistula tube was placed. The abscess resolved without complications.