Infant feeding is estimated to be responsible for 5%-20% of the burden of HIV transmission from mother to child. HIV positive women who cannot afford safe formula feeding are advised to practise exclusive breastfeeding (EBF) followed by prompt weaning. We conducted a qualitative study using observations and in-depth individual interviews to explore patterns of EBF as well as which factors motivate or hinder women to practice EBF. HIV positive women who intended to practice EBF from urban Malawi were purposively selected and interviewed. All women were well informed and had high knowledge on HIV as well as on EBF but much less knowledge on basic facts about breastfeeding. Despite their intentions less than half of the interviewed women managed to practice EBF and the barriers were explained by perceived lack of milk, lack of control over the feeding situation, felt and enacted stigma as well as poor counselling. Women who succeeded were older, had the explicit support of their husband and lived without the presence of their mother-in-law. Weaning at the age of 6 months was reported to be as difficult for the women as EBF. Intention itself is not a sufficient determinant of successful EBF unless a number of enabling factors come together. Prolonged breastfeeding is the cultural norm in Malawi and programs must be sensitive to social expectations to mothers and involve mothers-in-law and fathers in counselling of mothers who intend to practice EBF.