Data on 96 foster families with a foster child and a birth child between the ages of 10 and 21 years were used to analyze the association between support and conflict processes within the foster family and youths' reports on four indexes of well-being: self-esteem, self-efficacy, emotional problems, and behavioral problems. The self-esteem of foster children was more strongly affected by support and conflict processes in the foster family than was the self-esteem of birth children in the same family. For birth children as well as for foster children, parental support significantly related to emotional problems. For foster children, but not for birth children, more conflicts with the foster parents related to more behavioral problems. The results are compared with other studies, and implications for practice are suggested.