Background: In its recent report “Human Reproductive Technologies and the Law”, the House of Commons’ Select Committee on Science and Technology called for greater efforts to establish the potential demographic impact of sex selection across all sectors of UK society. Given the well-known preference for boys over girls among some communities, there is concern that a readily available service for social sex selection may upset the balance of the sexes. Of particular interest are the gen-der preferences and the demand for sex selection among Pakistanis. Materials and Methods: We conducted a social survey on gender preferences and demand for preconception sex selection among 301 pregnant women in Karachi, Pakistan, using a self-report ques-tionnaire consisting of 13 questions. Results: 41.5% wish to have a family with an equal number of boys and girls. 3.3% would like to have only boys, 1.0% only girls, 27.6% more boys than girls, 4.3% more girls than boys, and 22.3% stated that they do not care about the sex composition of their family. While 6.3% could imagine em-ploying cytometric sperm separation for social sex selection, 76.1% could not; 17.6% were undecided. 27.2% felt that social sex selection ought to be legal, 48.8% thought it ought to be illegal, and 23.9% were undecided. Abstract of the 8th Royan International Twin Congress, Tehran, Iran, 5-7 September 2007 42 Yakhteh Medical Journal, Vol 9, Sup 1, Summer 2007 Conclusion: Although Pakistani women do show a marked preference for boys over girls, the number of women will-ing to subject them selves to cytometric sperm separation appears to be too small to cause a severe imbalance of the sexes. However, further research among British citizens of Pakistani origin is needed to establish whether or not sex selection poses a serious threat to the sex ratio of UK communities.