Epidemiologic studies of pediatric rheumatologic disease are becoming increasingly focused on subfields of epidemiology. Genetic epidemiology is assuming an ever-greater role in the understanding of disease risks and pathogenesis. Such studies involve major histocompatibility complex, cytokine gene polymorphisms, T cell studies, and microarray-based expression technology. Clinical epidemiology, the study of occurrence and outcomes, increasingly relies on multicenter studies with data improving as study parameters become more standardized. With multicenter studies, there is an increasing trend to study ethnic differences in rheumatologic diseases of children.