Objective: To evaluate the impact of patient follicular environment with oxidative stress on oocyte quality. Methods: Patients on fertility treatment with either advanced maternal age or endometriosis were asked to donate follicular fluid collected during ovum pick-up. Follic-ular fluid (FF) was added (20%, 10% and 5%; %V/V) to in vitro maturation (IVM) medium with mouse oocytes. Following maturation culture, the oocytes were assessed for meiosis reinitiation. In a second setup, coenzyme Q10 was added to culture medium with FF. In addition to assessing meiotic maturation, a subset of oocytes was assessed for spindle structure and chromosome alignment. Results: Supplementation of IVM medium with FF of patients of advanced maternal age (with or without antiox-idants) did not have an effect on the maturation capacity of mouse oocytes. However, the addition of FF of individuals with endometriosis (without antioxidants) in the two highest concentrations affected oocyte maturation (61.5% & 57.0% maturation) compared with the lowest concen-tration (89.2% maturation) (p<0.05). Supplementation of medium with coenzyme Q10 did not improve the maturation rate of oocytes exposed to the FF of individuals with endometriosis (28.5±13.7%) (p<0.05). Nevertheless, preliminary analysis of spindle abnormality and chromosome alignment revealed that oocytes resuming meiosis in the presence of FF of patients with endometriosis displayed aberrant spindle morphology and chromosomal misalign-ment. Conclusion: The follicular environment of patients with endometriosis severely affected oocyte (nuclear) mat-uration. In vitro maturation in the presence of coenzyme Q10 appears to be a tool for rescuing oocytes exposed to such follicular environment.