A 38-yr-old nulliparous female presented with endometriosis of the terminal ileum which mimicked the clinical, roentgenographic, and surgical findings of Crohn's disease. The patient presented with diarrhea, right lower quadrant pain, fever, and significant weight loss. At surgery, the terminal ileum was inflamed, indurated, thickened, and angulated. Ileal endometriosis may be expected to simulate Crohn's disease, because intestinal endometriosis frequently produces local bowel inflammation, adhesions, stricture, and angulation. Ileal endometriosis should be carefully considered in the differential diagnosis of Crohn's disease in menstruating females who are nulliparous and have dysmenorrhea, dyspareunia, dyschezia, menometrorrhagia, or other perimenstrual symptoms. It is important not to mistake endometriosis for Crohn's disease because endometriosis has a different therapy.