Using Demographic and Health Survey data from 20 sub-Saharan African countries, this article compares the actual lengths of birth intervals to women's reported preferred lengths, and assesses the implications of the difference between the two for selected demographic and health indicators. The results show a clear pattern. In Comoros, Ghana, Kenya, Rwanda, and Zimbabwe, women prefer much longer birth intervals than those they actually have, compared with women in the other 15 countries studied. As a consequence, the potential effects of spacing preferences on the level of fertility and on the prevalences of short (less than 24 months) birth intervals and child malnutrition are greatest in the same five countries. The covariates of preferred birth-interval lengths are also examined. An explanation is offered for this pattern, based on the observed sharp decline infertility recently experienced by these five “forerunners.” In general, women who know, approve of, discuss, and use family planning prefer longer intervals than do their counterparts. The policy and program relevance of these results is discussed.