There is an ever increasing trend in reproductive medicine to reduce the intensity of ovarian stimulation for in vitro fertilization (IVF) and to restrict the number of embryos that are transferred into the uterine cavity. Recent findings suggest that the magnitude of ovarian stimulation affects the proportion of euploid embryos. As a result of the restriction in the number of embryos transferred, it becomes even more important to select the embryo with optimum implantational and developmental potential. Our aim was to asses the prevalence of numerical chromosomal abnormalities (aneuploidy) in unstimulated cycle IVF embryos. Thirty patients (mean age 31.4 years) underwent oocyte retrieval in a natural cycle without any form of ovarian stimulation, followed by intracytoplasmic sperm injection and Preimplantation genetic aneuploidy screening (PGS) for chromosomes X, Y, 13, 16, 18, 21 and 22. Out of 30 cycles, 21 oocytes were retrieved, 15 of which fertilized successfully. Eleven embryos developed sufficiently in order to undergo the PGS analysis, and four embryos proved to be aneuploid (36.4%; 95% CI: 10.9-69.2%). Six normal embryos were transferred in utero, resulting in three ongoing pregnancies. Two healthy girls were born and one patient miscarried. Numerical chromosomal abnormalities (aneuploidy) are present even in embryos of young women, and in the absence of ovarian stimulation.