Although endometriosis involves the small intestine only rarely, when present, this condition may stimulate a neoplasm clinically by producing intestinal obstruction or by forming a mass lesion. Five cases of ileal endometriosis are reported in this study. Three had produced localized intramural masses, resembling a neoplasm; one of these had also caused partial intestinal obstruction. Two other patients had diffuse involvement of a segment of ileum with mural thickening and luminal narrowing, leading to obstruction. The literature on small bowel endometriosis is reviewed and the clinical and pathological features are discussed.