We study the implications of the trade–off between child quality and child quantity for the efficiency of the rate of population growth. We show that if quantity and quality are inversely related then, even in the case of full altruism within the family, population growth is inefficiently high, if the family does not have, or does not choose to use, compensating instruments (for example, bequests or savings are at a corner). In non–altruistic models this trade–off certainly generates a population problem. We therefore prove that the repugnant conclusion is not only repugnant, it may be inefficient. Moreover, we cannot expect intra–family contracting to resolve the inefficiency since it involves contracts which are not credible.