This project investigated siblings' perceptions of family disruption when a brother or sister had cystic fibrosis (CF) or asthma. Data were gathered by phone interviews and questionnaires. Phone interviews were conducted with siblings of chronically ill children and employed open-ended questions focusing on the impact of the illness on the sibling and the family unit. Along with the interview, siblings also completed a separate self-esteem measure. Assessments of family functioning and demographic variables were obtained through parental questionnaires. Only the sibling interview data are addressed in this article. Fifteen families from the two illness groups participated. There were 6 male and 9 female respondents, with a mean age of 10.1 years. The average age of the well sibling was slightly older than the average age of the chronically ill child. For siblings of both disease groups, positive outcomes included strengthening some family relationships, achieving more personal independence, and experiencing satisfaction in seeing improvement in the ill child. Negative outcomes included worrying about the brother's or sister's illness, being jealous of the attention paid to the ill child, and the restriction of family events. Appropriate family interventions are suggested, as well as feedback as to the efficacy of phone interviews with school-age children.