In this study, 33% of the variance in the 10-year trend of forced expiratory volume in 1 second (FEV1), used as an index of pulmonary health, was explained by differences in family characteristics at the start of the study. Balanced family coping, a family emphasis on personal growth, and compliance with treatment for 91 children with cystic fibrosis were assessed at the start of the study and the FEV1 was observed at every clinic visit over the next 10 years. When both parents' coping emphasized family integration, support for self, and medical consultation, the FEV1 trend was better. Compliance with daily chest physical therapy and with quarterly clinic visits was associated with a better FEV1 trend. Poorer FEV1 trend was associated with active social involvement of family members. Older patients and patients whose parents worked more hours outside the home had lower compliance. These findings support the importance of encouraging families to balance their resources between the child's health needs and family needs.