Aim: To determine whether self-esteem among children with cystic fibrosis (CF) and their healthy siblings differs from that of a healthy reference group and whether there are differences within and between sibling pairs. Methods: All Swedish CF children 6-14 y old with a healthy sibling in the same age range (n = 65) were invited to participate, 55 sibling pairs and their parents taking part in the study. Five aspects of the children’ s self-concept-physical characteristics, skills and talents, mental well-being, relations to parents and family, and relations to others-were assessed by the “ I think I am” self-evaluation questionnaire. Severity of illness was assessed by means of the Shwachman Clinical Evaluation System. Results: Whereas self-evalua-tion did not differ between groups at a general level, healthy girls as well as those with CF scored lower than girls in the reference group on the “ mental well-being” and “ relations to parents and family” subscales. Comparison of gender combinations (sick girl/healthy boy, sick girl/healthy girl, sick boy/healthy boy, sick boy/healthy girl) suggested that girls pay a cost of a lesser sense of psychological well-being and feelings of inadequacy in relation to their parents and family. The Shwachman score of the sick child was not related to the level of self-esteem. Conclusion: When CF is present among siblings, girls seem to carry more of the family pain than boys, a finding that calls for an increased awareness of the girls’ situation by members of care teams. Aim: To determine whether self-esteem among children with cystic fibrosis (CF) and their healthy siblings differs from that of a healthy reference group and whether there are differences within and between sibling pairs. Methods: All Swedish CF children 6-14 y old with a healthy sibling in the same age range (n = 65) were invited to participate in 55 sibling pairs and their parents taking part in the study. Five aspects of the children’s self-concept-physical characteristics, skills and talents, mental well-being, relations to parents-and-family, and relations to others-were assessed by the “I think I am” self-evaluation questionnaire. Severity of illness was assessed by means of the Shwachman Clinical Evaluation System. -tion did not differ between groups at a general level, healthy girls as well as those with CF scored lower than girls in the reference group on the “mental well-being” and “relations to parents and family” subscales. Compariso n of gender combinations (sick girl / healthy boy, sick girl / healthy girl, sick boy / healthy boy, sick boy / healthy girl) suggested that girls pay a cost of a lesser sense of psychological well-being and feelings of inadequacy in relation to their parents and family. The Shwachman score of the sick child was not related to the level of self-esteem. Conclusion: When CF is present among siblings, girls seem to carry more of the family pain than boys, a finding that calls for an increased awareness of the girls’ situation by members of care teams.