Endometriosis is a benign pathology, commonly found in women at reproductive age. It is represented by the ectopic presence of the endometrial glandular epithelium in several tissues and organs. This ectopically located tissue can display premalignant or even malignant changes under the influence of certain factors that affect cell structure, function and proliferation. Our study includes a total of 28 patients, with endometriosis of different localizations: ovarian or pelvic endometriosis, adenomyosis or endometriosis of the abdominal wall. We performed a clinical and statistical analysis upon the collected clinical and laboratory data, together with the results obtained by using classical histological and immunohistochemical (IHC) profiling. The classical staining revealed the existence of the ectopic glandular epithelium, while the IHC reactions obtained with the anti-cytokeratin (CK) 7∕anti-CK20, anti-estrogen receptor alpha (ERα)∕anti-progesterone receptor (PR) antibodies, ascertained that these tissues were of endometrial origin. The environmental, hormonal or inflammatory factors influence these areas, so that the ER∕PR scores may be modified, the cellular proliferation might be increased (Ki67+ marker), the anti-apoptotic B-cell lymphoma 2 (BCL2) protein expression and phosphatase and tensin homolog (PTEN) may also be modified. Moreover, tumor protein 53 (p53) was positive in cases with atypia, density of inflammatory cells clearly increased compared to the adjacent normal endometrium, respectively with cluster of differentiation (CD) 3+, CD20+, CD68+, CD79a+, and tryptase+ cells, all of which may influence the cellular structure, histological architecture of the surrounding microenvironment and cause premalignant or even malignant changes in endometriosis outbreaks.