There are many challenges in coping with and adapting to life with a chronic disease, and increased survival cannot be assumed to be associated with increased quality of life. A recent systematic review shows there is wide variation in outcomes depending on the definitions and measurements used to estimate the prevalence of chronic health conditions, making the impact of disability on children's health and social functioning difficult to assess; various authors have called for an international consensus about the conceptual definition of chronic health conditions in childhood. It frequently is difficult to determine if problems in psychosocial functioning are caused by the underlying illness, by treatment, or by the resultant effects of either illness or treatment on physical growth or cognitive development. Assessment and treatment of mental health should be an integral component of the comprehensive care of chronically ill children and adolescents. Transition of care is an important process that addresses significant changes from child-oriented to adult-oriented care. Adults who have chronic health conditions should continue to be evaluated periodically for late consequences of the childhood illness and early medical care, and attention should be paid to their ongoing psychosocial, psychiatric, educational, and vocational needs.