The present randomized controlled in vitro study was designed to evaluate the effects of the exposure of human cryopreserved oocytes to endometriotic fluid. Twenty-three women aged 36 (4) years donated a total of 147 vitrified supernumerary metaphase II oocytes. Warmed oocytes were randomly assigned to exposure to endometriotic fluid or unexposed control. Thereafter, oocytes were parthenogenetically activated and cultured for up to 5 days. The rate of activation on day 1 and the developmental rates on days 3 and 5 did not significantly differ between the 2 groups. The rate of day 3 good quality parthenotes per oocyte was lower in exposed compared to unexposed oocytes, being 22% (13/60) and 41% (25/61), respectively. Moreover, in the exposed parthenotes, a significantly higher proportion of parthenotes failing to develop to the blastocyst stage showed cellular fragmentation (relative risk: 0.64, 95% confidence interval: 1.04-2.57). Exposure of human oocytes to endometriotic fluid has a negative effect on the morphology of deriving embryos/parthenotes mainly due to an excess of cellular fragmentation.