In adolescents with chronic illnesses, the rate of behavioral disorders is 10% to 20% higher than that in their well peers. Rheumatoid arthritis, chronic renal disease, cystic fibrosis, cancer, and many other chronic illnesses constitute risk factors for behavioral disorders in adolescents. Because they are now living longer, more productive lives, adolescents with chronic illnesses are more often seen by their primary care physicians with behavioral disorders that can interfere with disease control. Risk-taking behaviors, difficulties with parents, noncompliance, depression, and isolation may all be manifestations of behavioral disorders. Parents and siblings may also be at risk for disorder. Particular constellations of family and individual characteristics may be associated with behavior disorder. So that these behaviors may be discovered as early as possible, it is important that the primary care physician conceptualize chronically ill adolescents and their families as "at risk."