The aim of the study was to identify the pathomorphological features of the connective tissue component of the endometrium and the junctional zone of the uterus in adenomyosis in women of late reproductive age. Materials of the study were fragments of endometrium with the subject myometrium, which were obtained by hysteroscopic surgical intervention with subsequent mechanical evacuation of the tissue and conducting its histological examination. Depending on the nature of the pathological process in the resulting biopsy material, the patients were divided into the following groups: I group consisted of 18 cases of adenomyosis I–II degree, II group — 6 cases of endometrial hyperplasia, group III — 6 cases of glandular fibrotic polyp of endometrium, IV group — 6 cases of glandular-fibrous polyp on the background of glandular hyperplasia of the endometrium. In all the groups (the study group and the comparison group), in addition to the stroma, collagen fibers were detected along the basement membranes of the glands and blood vessels. As for the myometrial part of the junctional zone, collagen fibers surrounded the tufts of smooth muscle fibers. In adenomyosis, smooth muscle fibers are slightly enlarged in comparison with the comparison groups. It has been established that the stroma of the endometrium and the junctional zone in adenomyosis and some proliferative processes of the endometrium differ both in the survey microscopic pattern and in the number and location of collagen fibers, which may be one of the differential criteria between the pathological processes studied in this study.