Objective — to investigate the expression of moesin, p21-activated kinase 4 (PAK 4), matrix metalloproteinases (MMP 2, MMP 9), and CD34 in the eutopic and ectopic endometrium in different forms of adenomyosis. Material and methods. Fifty uteri removed for diffuse adenomyosis and for adenomyomas were examined in reproductive-aged (n=25) and premenopausal (n=25) women. A comparison group included 20 uteri removed for intramural and subserosal fibroids in reproductive-aged and premenopausal women. The investigators performed histological and immunohistochemical (using antibodies to moesin, PAK 4, MMP 2, MMP 9, and CD34) examinations of the eutopic and ectopic endometrium. Results. Different forms of adenomyosis were characterized by the irregular border of the endometrium and myometrium due to that there were multiple foci of ingrowth of the basal layer of the endometrium through the terminal plate into the myometrium. In both diffuse adenomyosis and adenomyomas, the basal layer of the eutopic and ectopic endometrium differed many (3—8.5) times, showing the higher expression of the enzymes in the epithelial and stromal cells, which affected their invasive activity (moesin, PAK 4, MMP 2 and MMP 9), and the increased number of CD34 cells in its stroma. At the same time, there were no statistically significant differences in their expression in the basal layer of the eutopic and ectopic endometrium in diffuse adenomyosis and adenomyomas. Conclusion. The findings favor the theory of the pathogenesis of adenomyosis due to the invasion of the eutopic endometrium into the myometrium.