Endometriosis is an estrogen-dependent chronic inflammatory disease that causes infertility and pelvic pain. The mechanisms of associated infertility remain unknown. A few of the earlier hypotheses proposed include anatomical changes and tubal obstruction due to pelvic adhesions, as well as several other factors such as inflammatory cytokine-mediated impairment of endometrial permissiveness and oocyte mass. The ovarian aspect of this disease has been shown to have a detrimental effect on ovarian physiology. Indeed, ultrasound and histologic data tend to support a reduced number of ovarian follicles in patients with endometriosis. In addition, the local environment of the follicles in patients is significantly different from that of the healthy population, as evidenced by alterations in the granulosa cells, including a decrease in aromatase-expressing P450 and an increase in intracellular reactive oxygen species production. Oocytes obtained from women affected by endometriosis were more likely to fail to mature in vitro and show altered morphology and reduced cytoplasmic mitochondrial content compared to patients with other causes of infertility. The results of the meta-analysis suggest that a reduced number of mature oocytes is associated with endometriosis and that reduced fertilization rates may begin at milder disease levels. However, this still lacks sufficient, robust evidence and requires further study.