Until recently, relatively little was known about the background risk of malignancy in pediatric rheumatic diseases. Worrying reports about the development of malignancies in children treated with new biologic agents have prompted rigorous studies of the incidence of malignancy associated with juvenile idiopathic arthritis (JIA). These studies reveal that JIA is likely to be associated with an increased risk of incident malignancy, irrespective of treatment with new biologic agents. A preliminary study indicates that the background risk of malignancy is also elevated in pediatric-onset systemic lupus erythematosus. On the basis of simple observation, the background risk of malignancy among children with Sjögren syndrome and dermatomyositis seems much lower than the markedly elevated risk found in adults with the same diagnoses. Clearly, the background risk of malignancy must be considered in any evaluation of the safety of new therapeutic agents.