Objective - To describe self-reported treatment adherence among people with type 1 diabetes treated with insulin and/or oral antidiabetic medications and to identify its determinants. Patients and Methods - A total of 8,926 people with diabetes were randomly selected from among beneficiaries of the General Scheme for Salaried Workers and the Social Scheme for the Self-Employed, residing in metropolitan France, aged at least 18 years as of July 31, 2007, and who had received at least three reimbursements for oral antidiabetic medications and/or insulin during the previous 12 months. A self-administered questionnaire was sent to all selected individuals, and treatment adherence was assessed using six validated questions. The response rate to the self-administered questionnaire was 48%, with 4,277 questionnaires returned. Logistic regression with a stepwise upward selection procedure, accounting for the sampling design and non-response (weighting), was used to identify the determinants of treatment adherence. Results - Treatment adherence was assessed in 237 patients with type 1 diabetes, with a mean age of 42 years (range 18–73 years) and comprising 49% men. Therapeutic adherence was good in 28%, moderate in 55%, and poor in 17% of cases. In multivariate analysis, the factors associated with poor adherence were, in descending order of importance: a doctor-patient relationship in which the patient reported making decisions alone (OR = 6.4; 95% CI [1.4–29.4]), age under 25 years (OR = 4.9; 95% CI [1.1–21.7]), a body mass index greater than 30 kg/m² (OR = 4.7; 95% CI [1.3–16.8]), financial difficulties (OR = 4.4; 95% CI [1.3–15.5]), and perceiving the implementation of diabetes management recommendations as too burdensome (OR = 3.9; 95% CI [1.2–12.8]). Conclusion - This analysis characterizes treatment adherence among patients with type 1 diabetes at the national level. Understanding its determinants may help tailor care for patients most likely to have poor adherence, particularly through an educational approach or support. Paper cited in the journal "Diabetes and Metabolism" in Supplement 1, Volume 36.