Endometriosis is a common gynecological disorder of the reproductive age characterised by pelvic pain, dysmenorrhea and infertility. Classic theories have failed to propose a precise pathogenetic mechanism. Recent studies have investigated the role of the immune system and oxidative stress in the development of endometriosis as well as the identification of biomarkers for a non-invasive diagnosis of the disease. At endometriotic sites, inflammatory cells including eosinophils, neutrophils and macrophages generate reactive oxygen species that contribute to the development of oxidative stress in the peritoneal cavity. Oxidative stress further augments immune response in affected sites. The oxidants exacerbate the development of endometriosis by inducing chemoattractants and endometrial cell growth-promoting activity. The oxidative proinflammatory state of the peritoneal fluid is an important mediator of endometriosis. Many studies investigate the correlation of endometriosis and oxidative stress but the results are discrepant. Furthermore, oxidative stress has been implicated in unexplained infertility and has been associated with some of its causative factors. Oxidative stress influences women's reproductive capacity. The association between endometriosis and infertility is described in several studies and still remains debated.