Endometriosis is a gynecological inflammatory and estrogen dependent pathology, defined as the presence of endometrial tissue outside the uterine cavity. The two most common symptoms of endometriosis are pelvic pain and infertility. This pain can be so intense that it affects the quality of life of women, from their relationships to their daily activities. Approximately 10% of women of reproductive age suffer from this disease. The main objective of this work was to investigate which immune system abnormalities present in patients with endometriosis that prevents ectopic endometrial tissue removal. Here we describe a series of changes in the different types of leukocytes, cytokines and factors that regulate the immune response seen in patients with endometriosis and the mechanisms by which these changes, not only favor "immunological tolerance" to the endometrial implants but at the same time stimulate the development of the disease by increasing cell proliferation and angiogenesis and inhibition of apoptosis ectopic endometrial tissue.