Children with a parent who suffers from depression are at raised risk for the disorder themselves. Relatively little is known about the development of psychological vulnerability to depression through childhood, particularly during infancy and early childhood. This paper describes results from a longitudinal prospective study of the development of children, studied from birth to 16 years, of mothers who experienced postnatal depression; it highlights the roles of the developing mother-child relationship, and of physiological functioning and social relationships in the development of adolescent vulnerability.