Objective — to compare the data of morphological evaluation and results of PGS.  Material and methods. We studied 116 couples who got PGS on 5, 7, 10 chromosomes using the FISH method. Results. 688 embryos were analyzed genetically and morphologically. They were qualified as excellent, good and bad quality according to morphological criteria. PGS was performed for each group. All embryos with numerical chromosome anomalies were divided into 2 groups: sublethal and lethal. We show that the best quality embryos have normal chromosome set at 57% on day 3 and 80% on day 5 of development. Conclusions. Embryos that would have been selected for transfer according to morphological criteria and without using PGS, in 30% of cases knowingly carry chromosomal pathology, which can cause IVF failure, miscarriage or birth of a sick child.