Abstract Endometriosis of the bowel is of sufficiently frequent occurrence to warrant emphasis of the characteristic symptoms by review of a case in which the correct preoperative diagnosis was made, but only after acute obstruction had supervened. Publication of detailed clinical and pathological follow-up examinations is advisable to ascertain more accurately the fate of endometriomas of the bowel which have been treated by castration without resection. ∗ ∗ Since this paper was submitted for publication, an unmarried woman of thirty years was admitted to St. John's Hospital May 11, 1941, for treatment of dysmenorrhea and constipation. At operation a large chocolate cyst of the left ovary, rectovaginal and uterine endometriosis, and an almost completely obstructing endometrioma of the midsigmoid colon were treated by bilateral salpingo-oophorectomy, supravaginal hysterectomy and obstructive resection of the sigmoid. Distinct invasion of the mucosa was demonstrated grossly and microscopically. Complete situs inversus was an incidental finding.