Endometriosis in the groin is a rare condition which may cause diagnostic problems. It occurs in women of reproductive age and it often takes several years before the correct diagnosis is made. The condition is found most often in association with ligamentum rotundum. Lesions may be dark or pale, hard or rubbery, and often infiltrate surrounding tissue. Treatment is surgical excision. The author describes four cases seen in the course of two years. They illustrate the typical features of this condition and were diagnosed by exploratory surgery. Endometriosis in the groin may be less rare than previously assumed, and early surgical exploration is recommended in women with a painful lump in the inguinal region.