Although evidence suggests that long term illness in a child is a significant stress on family members, few studies of family adaptation to childhood illness have assessed how ill children's healthy siblings understand and respond to this unique life stress. The present study investigated whether the experience of living with a chronically ill sibling was related to young adults' beliefs regarding locus of control of health, perceptions of vulnerability to illness, and attributions concerning causes and prevention of illness. Twenty-seven experimental and 27 control subjects were assessed with the Multidimensional Health Locus of Control Scale, Likelihood of Illness Scale, Vulnerability to Illness Questionnaire, and the Concept of Illness Task. In addition, experimental subjects were assessed with descriptive measures regarding their retrospective and current perceptions of the impact of chronic sibling illness on their lives. Results of both quantitative and qualitative data analyses indicated that living with a chronically ill sibling during childhood has a powerful effect on young adults' conceptualizations of illness and goals for the future. Healthy siblings of chronically ill children demonstrated a stronger belief in chance determining health and illness than did matched individuals who had not lived with an ill sibling. The experience of living with an ill sibling was also associated with young adults' beliefs in the prevalence of illness in the general population as well as with differential attributions for the causes and prevention of illness. In addition, the experience of caring for an ill sibling was associated with choosing majors in college which would prepare young adults for "helping" professions. These findings were discussed in relation to previous research by the author examining latency age siblings' responses to childhood illness. A comparison of both studies revealed the specific burdens that chronic illness places on family members as well as a complex interplay of adaptive strategies utilized by the well sibling and the family. Implications of findings on the developmental changes in well siblings' response to chronic childhood illness were discussed in regard to future research and intervention.
