The present investigation explored the association of mother--child and father--child emotional expressiveness during toddlerhood to children's prosocial and aggressive behaviour with peers. Data were collected from 62 Mexican-American families with toddlers (29 females, 33 males) during a home visit. Children's peer interactions were also observed approximately eight months later at their child-care setting. Observed mother--child and father--child interaction was coded for positive and negative emotional expressiveness, including shared positive and negative emotion. Observed child--peer interactions were coded for prosocial and aggressive behaviour. Data revealed that mother and father's expression of positive and negative emotion were uniquely related to children's prosocial and aggressive behaviour with peers. Children's expression of negative emotion with mothers and fathers was related to higher levels of peer aggression. Mother--child shared positive emotion predicted less peer aggression, whereas mother--child shared negative emotion predicted less prosocial behaviour and more peer aggression. Father--child shared positive emotion predicted more prosocial behaviour and less aggression. The associations between dyadic measures of parent--child shared emotion and peer interaction variables were significant even after the variance accounted for by the individual parent and child emotional expressiveness variables were included in regression equations. This suggests that the shared emotion measure captures a quality of the parent--child relationship that has links to children's social adjustment with peers extending beyond the individual behaviour of either parent or child. The role that mother--child and father--child emotional expressiveness may play in children's development of peer interaction skills is discussed. (Contains 3 tables.)