Parental communication and support is associated with improved developmental, health and behavioral outcomes in adolescence. This study explores the quality of mother-daughter communication about sexual maturation, abstinence and unintended pregnancy in Korogocho, an informal settlement in Nairobi, Kenya. We use data from 14 focus group discussions (n = 124) and 25 interviews with girls aged 12-17, mothers of teenage girls, and key informant teachers. Many girls and women believed that mothers are the best source of information and support during puberty but only a minority described good experiences with communication in practice. Girls preferred communication to begin early and be repeated regularly. Mothers often combined themes of sexual maturation, abstinence and avoiding pregnancy in their messages. Communication was facilitated by mothers' availability, warmth and close parent-child relationships. Challenges included communication taboos, embarrassment, ambiguous message content, and parental lack of knowledge and uncertainty. Neighborhood poverty undermined some mothers' time and motivation for communicating.