Background: In patients with juvenile idiopathic arthritis (JIA), growth impairment and altered body composition, including disturbed skeletal development, are well-known long-term complications. Data on longitudinal growth in patients with systemic and polyarticular JIA reveal growth impairment in the active phases of the disease. With reduction in disease activity and lower glucocorticoid (GC) doses, some patients experience ‘catch-up’ growth; however, many have only a slight improvement in height standard deviation during puberty or after cessation of GC treatment. The consequence is a final height below the 3rd percentile and below the genetic height potential. Although few studies have specifically addressed body composition in children with JIA, studies on the development of bone mass have described notable deficits in both GC-treated and GC-naïve children. In recent years, the deficits in bone mass have been related, in part, to the deficits in muscle mass, which are prevalent in these patients. Conclusions: The major goal for physicians caring for patients with JIA is optimal disease control while maintaining normal growth. Early recognition of patients who develop prolonged growth disturbances and altered body composition is important as these abnormalities contribute to long-term morbidity and need to be addressed both diagnostically and therapeutically when treating children with JIA.