SEARCH for Diabetes in Youth is an observational, multicenter study focusing on physician-diagnosed diabetes in individuals <20 years old. The study will estimate the population prevalence and incidence of diabetes by type, age, gender, and ethnicity and develop practical approaches to diabetes classification in 5 million children ( approximately 6% of the <20 U.S. population) with wide ethnic and socioeconomic representation from four geographically defined populations and two health plans. An estimated 6000 prevalent and 800 incident diabetes cases per year will be identified with annual follow-up. Cases will be ascertained through clinical and nonclinical resources or partnerships at each site. Data collection involves patient interviews, physical examinations, laboratory measurements (diabetes autoantibodies, fasting/stimulating C-peptide, hemoglobin A1c, blood glucose, lipids, urine albumin, creatinine), medical records reviews, and documentation of risk factors for complications and processes of care.