The rate of HIV transmission via breast-feeding ranges from 14% to 26%, depending on the timing of maternal infection. In settings where infant mortality rates from infectious diseases and malnutrition are low and relatively safe alternatives to breast-feeding are available, HIV-infected mothers should be advised not to breast-feed. Where breast-feeding by HIV-infected mothers and bottle-feeding both present serious risks of mortality, changing the conditions in which families live so that safe feeding alternatives become available must be a top priority. At the same time, these mothers need information about the relative risks and benefits of breast-feeding, early weaning, wet-nursing, and formula feeding. This article reviews the available research data and discusses critical gaps in current knowledge.