CONTEXT: The T1D Exchange includes a clinic-based registry, a patient-centric web site called Glu, and a biobank. OBJECTIVE: The aim of the study was to describe the T1D Exchange clinic registry and provide an overview of participant characteristics. DESIGN: Data obtained through participant completion of a questionnaire and chart extraction include diabetes history, management, and monitoring; general health; lifestyle; family history; socioeconomic factors; medications; acute and chronic diabetic complications; other medical conditions; and laboratory results. SETTING: Data were collected from 67 endocrinology centers throughout the United States. PATIENTS: We studied 25,833 adults and children with presumed autoimmune type 1 diabetes (T1D). RESULTS: Participants ranged in age from less than 1 to 93 yr, 50% were female, 82% were Caucasian, 50% used an insulin pump, 6% used continuous glucose monitoring, and 16% had a first-degree family member with T1D. Glycosylated hemoglobin at enrollment averaged 8.3% and was highest in 13 to 25 yr olds. The prevalence of renal disease was =4% until T1D was present for at least 10 yr, and retinopathy treatment was =2% until T1D was present for at least 20 yr. A severe hypoglycemic event (seizure or coma) in the prior 12 months was reported by 7% of participants and diabetic ketoacidosis in the prior 12 months by 8%. CONCLUSIONS: The T1D Exchange clinic registry provides a database of important information on individuals with T1D in the United States. The rich dataset of the registry provides an opportunity to address numerous issues of relevance to clinicians and patients, including assessments of associations between patient characteristics and diabetes management factors with outcomes.