In the literature, the problems of the histology, morphogenesis and malignant transformation of ovarian endometriosis are being elucidated but rather contradictory. The author's personal study is based on the examination of operative materials from 228 patients. There was found heterogenicity of the microscopic structure of ovarian endometriosis, and its following variants were revealed: a) in relation to the growth-progressive, stable, regressive malignant; b) in relation to the spread-focal, diffuse, unilateral, bilateral, with extraovarian dissemination, without extraovarian dissemination; c) in relation to the morphology-glandular, adenocystic, cystic, stromal. A detailed morphological characteristic is given of malignant transformation of ovarian endometriosis, observed in 26 cases.