This study examined the challenges that HIV-positive women face at different stages of early infant feeding using a longitudinal, qualitative design. The study explored factors influencing infant-feeding decision-making and behavior of HIV-positive mothers and identified characteristics of women and their environments that contributed to success in maintaining exclusivity of their infant feeding practices. The study was undertaken at 3 sites in South Africa. Participants consisted of a purposive sample of 27 women who had a positive HIV test result during antenatal care and were intending to either exclusively breast-feed or exclusively formula-feed their infants. Women were interviewed once antenatally and at 1, 4, 6, and 12 wk postpartum. Just under one-half of the women who initiated breast-feeding maintained exclusivity and over two-thirds of the women who initiated formula-feeding maintained exclusivity. Key characteristics of women who achieved success in exclusivity included the ability to resist pressure from the family to introduce other fluids and to recall key messages on mother-to-child transmission risks and mixed feeding. Among women who maintained exclusive breast-feeding, a strong belief in the benefits of breast-feeding and a supportive home environment was important. For women using formula milk, having resources such as electricity, a kettle, and flask made feeding at night easier. Support for infant feeding that extends beyond the antenatal period is important to enable mothers to cope with new challenges and pressures at critical times during the early postpartum period.