This study assessed the development of independence and its interaction with some biologic factors. Sixty-four adolescents with cystic fibrosis (CF) were compared with 36 adolescents with bronchial asthma, 47 healthy but small adolescents, and 71 normal healthy controls. A structured interview was designed to measure eight elements of independence. Adolescents with CF showed less responsibility for their own body hygiene and a delay in intimacy and sexuality, both correlated with puberty not yet having started. They also took less part in a number of social activities outside the home. There were minimal or no differences between ill and healthy adolescents for four elements. The results indicated that in future research, different types of independence should be taken into account. The correspondences between the chronically ill and the healthy adolescents prevailed over the differences. The main differences could be interpreted in terms of realistic coping with the illness and maintaining hope for the future.