Self-management of a chronic illness involves not only monitoring symptoms, adhering to medication regimens, and keeping medical appointments but also making and maintaining difficult lifestyle changes. This article highlights correlational and intervention research suggesting family members are influential in children’s and adults’ illness management. The argument is made that a dyadic approach to chronic illness management that targets the influence of close relationships may yield more sustainable effects on patient behavior than has been achieved in the past. In particular, dyadic approaches aimed at helping patients and family members to find ways to collaborate in goal setting for these behaviors is recommended. Such dyadic interventions may also benefit family members who are ill or are at risk because of poor health behaviors.