Introduction: The current revised classification system of endometriosis, proposed by the American Society for Reproductive Medicine (ASRM), is simple, flexible enough to describe any case and offers a useful tool in routine practice, recording at the same time an analytical and descriptive footprint of patient's situation. However, it lacks general consensus and is criticized for multiple reasons, including poor correlation with pelvic pain and infertility as well as limited reproducibility of the staging. Several potential modifications to the existing classification system have been proposed based on pathological factors, biomarkers and imaging findings. Nevertheless, as the challenge of creating a satisfactory classification of endometriosis remains, we focused on a newly recognized multifunctional factor involved in endometriosis and investigated the role of Bone Morphogenetic Protein 6 in association with ASRM classification system. Materials and Methods: After inclusion and exclusion criteria, eighty six consecutive women suffering by endometriosis of stages I to IV were enrolled as the observation group and 40 non endometriosic served as the control group in this prospective study. All women underwent gynecological operations due to ovarian cyst presence. Tissue specimens were collected from ectopic endometriotic lesions and ovaries, and Bone morphogenetic protein 6 (BMP-6) expression was evaluated by immunochemical staining and PCR method. Results: Compared with the control group, women with endometriosis demonstrated significantly higher expression of BMP 6 (p_0,000). Moreover, there was a significant correlation between BMP6 immunoreactivity in both epithelium and stroma with staging and scoring record of endometriosis according to ASRM classification system in the order of IV_III_II_I. Conclusion_ BMP-6 has a multidimensional role in cell development and differentiation and recent studies propose that may be at least partly involved in the mechanisms of attachment, survival and expansion of endometriosis. In the present study we demonstrate that BMP 6 expression is strongly correlated with existing staging of endometriosis system. Therefore, we propose that routine measurement of BMP-6 could be a useful addition in existing ASRM classification system.