SummaryThe discussion presented here is intended to clarify some of the problems arising in an analysis of the possible effects of birth control on the human sex ratio. Formulas are presented indicating some of the ways in which the sex ratio can be modified as a result of the use of birth‐control methods. These formulas lead to different conclusions from those presented in the earlier literature on this subject. Further empirical research, along lines suggested by the considerations arising from the present discussion, is needed. The overall effect of birth control on the sex ratio will depend upon, among other things, the particular kinds of preferences for male offspring that influence the married couples in the population, the particular kinds of preferences for female offspring that influence the married couples in the population, the particular ways in which these preferences affect the parents' decisions as to whether or not to have another child (if they make such decisions), the relation between the parents' decisions and their probability,pt, of bearing a boy, the effectiveness with which these decisions are carried out, the relation between family size andpitthe distribution of thepiin the population, and the nature of thev