Current biomedical research on sex selection techniques may soon offer couples the opportunity to choose the sex of their children with greater certainty. A technique planned for marketing by mid-I978 can increase the probability of bearing a son to as much as 0.90. However, couples who wish to improve their chances of bearing a daughter have no such opportunity. The purpose of this paper is two-fold. First, a decision-making model is provided which describes how couples should choose among alternative sex-selection methods so as to maximize the probability of bearing their desired number of sons and daughters. Second, the effect of the widespread use of sex-selection techniques on the population sex ratio is explored. It is shown that even if populations have unbiased sex preferences, or sex preferences biased towards daughters, the use of biased sex-selection technologies may result in very high population sex ratios.