paternal involvement in organizational/care tasks and play/leisure activities was studied in a sample of dual-earner portuguese families, with children that attend day-care for several hours a day. socio-demographic variables were analysed in relation to involvement, as well as the impact of father’s participation in children’s organization of secure base behaviour in mothers and fathers relationships. 44 mother/child and father/child dyads participated in the study, children’s average age was 31.91 months (dp=2.56). to assess paternal involvement, (relative measure), both parents answered separately a questionnaire (monteiro, veríssimo, castro, & oliveira, 2006). the quality of the children’s secure base behavior was assessed with the attachment behavior q-set (waters, 1995). mother/child and father/child dyads were observed, separately, in their homes, by different teams of observers. a traditional division in organization/care and a shared participation in the play activities emerged. no significant correlations were found between socio-demographic variables and fathers participation. fathers that shared caregiving and play activities with mothers have children with higher security scores. in this sample the quantity of father’s participation showed positive consequences for the child socio-emotional development.