During the last 15-year period in our laboratory, 14 cases of malignant change of endometriosis were diagnosed in women 37-70 years of age. Seven cases were adenocarcinomas, one case was an adenosarcoma and six cases presented the morphology of endometrial stromal sarcoma. Eleven cases developed in various sites of the genital system (5/11 in the ovaries, 3/11 in the uterus 2/11 in the vagina, 1/11 in the tubal wall) and three cases in extragenital sites (1/3 in the omentum, 1/3 in the pelvis, 1/3 in the colon). Immunohistochemical investigation for the expression of cytokeratines, vimentin, hormonal receptors, E-cadherin, desmine and smooth muscle actin was performed by a streptavidin-biotin method. The immunopathology profile and follow-up results after therapy are presented.