OBJECTIVE Celiac disease (CD) has a recognized association with type 1 diabetes.We examined international differences in CD prevalence and clinical characteristics of youth with coexisting type 1 diabetes and CD versus type 1 diabetes only. RESEARCH DESIGN AND METHODS Data sources were as follows: the Prospective Diabetes Follow-up Registry (DPV) (Germany/Austria); the T1D Exchange Clinic Network (T1DX) (U.S.); the National Paediatric Diabetes Audit (NPDA) (U.K. [England/Wales]); and the Australasian Diabetes Data Network (ADDN) (Australia). The analysis included 52,721 youths <18 years of age with a clinic visit between April 2013 and March 2014. Multivariable linear and logistic regression models were constructed to analyze the relationship between outcomes (HbA1c, height SD score [SDS], overweight/obesity) and type 1 diabetes/CD versus type 1 diabetes, adjusting for sex, age, and diabetes duration. RESULTS Biopsy-confirmed CD was present in 1,835 youths (3.5%) and was diagnosed at a median age of 8.1 years (interquartile range 5.3-11.2 years). Diabetes duration at CD diagnosis was <1 year in 37% of youths, 1-2 years in 18% of youths, 3-5 years in 23%of youths, and 5 years in 17%of youths. CD prevalence ranged from1.9%in the T1DX to 7.7%in the ADDNand was higher in girls than boys (4.3%vs. 2.7%, P < 0.001). Children with coexisting CDwere younger at diabetes diagnosis compared with those with type 1 diabetes only (5.4 vs. 7.0 years of age, P < 0.001) and fewer were nonwhite (15 vs. 18%, P < 0.001). Height SDS was lower in those with CD (0.36 vs. 0.48, adjusted P < 0.001) and fewer were overweight/obese (34 vs. 37%, adjusted P < 0.001),whereasmeanHbA1c valueswere comparable: 8.361.5%(67617mmol/mol) versus 8.4 6 1.6% (68 6 17 mmol/mol). CONCLUSIONS CD is a common comorbidity in youth with type 1 diabetes. Differences in CD prevalence may reflect international variation in screening and diagnostic practices, and/ or CD risk. Although glycemic control was not different, the lower height SDS supports close monitoring of growth and nutrition in this population.