Adenomyosis and Endometriosis are not the same condition, but currently ICD-10 presents adenomyosis as a variety of endometriosis with the code N80.0 and usually the differences between them are not given proper attention. In ICD-11 these two pathologies will be found as different identities with the codes GA10 and GA11. The purpose of the research was to find in the scientific international literature morphological differences between adenomyosis and endometriosis. The PubMed, Springer Link and Google Scholar databases were used to identify information linked to this topic. Actually, adenomyosis is limited completely to stay within the uterus and usually affects older women. Howev endometriosis does not develop within the uterus, and if it does, it may be rare and usually occurs with adolescents and women of reproductive age, both follow the menstrual cycle, bleeding monthly. Adenomyosis and endometriosis are usually regarded as closely related, but microscopic appearance, and probably their pathogenesis, are somewhat different, they may occur independently of each other and adenomyosis mostly is made up of nonfunctional (basal) endometrium and frequently connected with the mucosa (versus endometriosis, composed of functional layers). In adenomyosis glandular tissue usually is inactive and of basalis or proliferative type endometrium which is not specific for endometriosis. adenomyosis ectopic nests of endometrial glands and stroma within the myometrium are surrounded by reactive smooth muscle hyperplasia, in endometriosis there are blue cystic nodules which are surrounded by fibrosis. Although adenomyosis and endometriosis have several similarities in clinical aspects and morphology, however, there are some particularities that make them different pathologies. These should be considered in order to have a better understanding of the disease and to approach more effective clinical management. Definitive distinction between these pathologies requires further studies.