Introduction Little evidence exists on breastfeeding and infant feeding practices in urban slums in sub-Saharan Africa. Our aim was to assess breastfeeding and infant feeding practices in Nairobi slums with reference to WHO recommendations.

Methods Data from a longitudinal study conducted in two Nairobi slums are used. The study involves 4299 children aged 0–42 months, born between September 2006 and January 2010, for the period they were infants. All women who gave birth during this period were interviewed on breastfeeding and complementary feeding practices at recruitment and this information was updated twice, at 4-monthly intervals. Cox proportional hazard analysis was used to determine factors associated with cessation of breastfeeding in infancy and early introduction of complementary foods.

Results There was universal breastfeeding with almost all children (99.0%) having ever been breastfed, and 85% were still breastfeeding by the end of the 11^th month. Exclusive breastfeeding for the first 6 months was rare (2%). Factors associated with sub-optimal infant breastfeeding and feeding practices in these settings include child's sex; perceived size at birth; mother's marital status, ethnicity, and education level; pregnancy desirability; place of delivery; and slum of residence.

Conclusions The study indicates poor adherence to WHO recommendations for breastfeeding and infant feeding practices. Breastfeeding and infant feeding patterns are associated with child, maternal and household level characteristics. Interventions and further research should pay attention to factors such as cultural practices, access to and utilisation of healthcare facilities, child feeding education, and family planning.