Objective To demonstrate the use of the actor–partner interdependence model (APIM) of dyadic relationships in a sample of children with cystic fibrosis (CF) and their caregivers. Methods Multilevel modeling evaluated relations between health-related quality of life (HRQOL) and anxiety in 29 child–caregiver dyads. The following effects were evaluated: actor and partner, and the respondent (i.e., child or caregiver) x HRQOL interaction. Results This study demonstrated a practical application of the APIM. Significant actor effects were found (i.e., lower child HRQOL was associated with increased child anxiety, caregiver anxiety increased as caregiver perceptions of their child’s HRQOL decreased), but not partner effects. The significant interaction indicated that the effects were different for children and caregivers. Conclusions The APIM has the potential to increase pediatric researchers’ understanding of how social relationships and environments impact health outcomes. Future research should consider using dyadic data analysis when youth and caregiver data are available.