Sex selection is possible with the use of cell sorters, followed by artificial insemination. Sex determination is feasible also by FISH or PCR before implantation. The mammalian X-chromosome-bearing sperm has 2.8 to 7.5% more DNA than the Y bearing sperms. The sperm can be classified and selected with high efficiency and at high speed (18 million sperm/h). It is used in animal husbandry for artificial insemination and its effectiveness is 85–95%. It would be technically feasible also in human artificial insemination and ethically less objectionable than the preimplantation selection of fertilized eggs. Sex selection involves not just ethical problems but it may also affect the sex ratio in the population. It has been estimated that in China the males exceed females by ∼30% because of selective abortion. This also leads to a social imbalance because many males may not find mates. cell sorter, segregation distorter, sex determination, ART, PGD, social selection, sex ratio; Garner DL 2001 J Androl 22:519; Johnson LA 2000 Anim Repr Sci 60–61:93; van Munster EB 2002 Cytometry 47:192; Welch GR, Johnson LA 1999 Theriogenology 52:1343; international survey of frequency: Sermon K et al 2005 Hum Reprod 20:19.