AbstractAimsTo examine educational outcomes among adolescents with type 1 diabetes and determine the role of comorbidity.MethodsWe conducted a nationwide register‐based cohort study including 3370 individuals born between 1991 and 2003 and diagnosed with type 1 diabetes before the age of 16. They were all matched with up to four individuals without type 1 diabetes on age, gender, parents' educational level and immigration status. Information on comorbidity was based on hospital diagnoses. The individuals were followed in registers to determine whether they finished compulsory school (9th grade, usually at the age of 15–16 years), and were enrolled in secondary education by age 18 years.ResultsIndividuals with type 1 diabetes were more likely not to complete compulsory school (OR 1.44, 95% CI 1.26–1.64), and not being enrolled in an upper secondary education by age 18 (OR 1.50, 95% CI 1.31–1.73) compared to their peers. A total of 1869 (56%) individuals with type 1 diabetes were registered with at least one somatic (n = 1709) or psychiatric comorbidity (n = 389). Those with type 1 diabetes and psychiatric comorbidity were more likely not to complete compulsory school (OR 2.47, 95% CI 1.54–3.96), and not being enrolled in an upper secondary education by age 18 (OR 3.66, 95% CI 2.27–5.91) compared to those with type 1 diabetes only. Further, there was a tendency towards an association between having somatic comorbidity and adverse educational outcomes (OR 1.25, 95% CI 0.97–1.63; OR 1.26, 95% CI 0.95–1.66) among adolescents with type 1 diabetes. The associations differed markedly between diagnostic comorbidity groups.ConclusionType 1 diabetes affects educational attainment and participation among adolescents. Psychiatric comorbidity contributes to adverse educational outcomes in this group, and there is a tendency that somatic comorbidity also plays a role.