OBJECTIVE: To assess the effect of the insulin analog detemir on glycemic control and severe hypoglycemia in children and adolescents with type 1 diabetes. RESEARCH DESIGN AND METHODS: A retrospective chart analysis was performed in 105 patients with type 1 diabetes after switching to insulin detemir between 2004 and 2007. In children below 12 yr of age (n = 53), evening neutral protomin hagedorn (NPH) insulin was replaced by insulin detemir if therapeutic goals were not reached and blood glucose levels were unpredictable or hardly controllable. In adolescents above 12 yr of age (n = 52), insulin detemir was started when changing to intensified insulin therapy. RESULTS: In children below 12 yr of age, hemoglobin A1c (HbA1c) at start was 8.3 +/- 0.8% and after 12 months of treatment with insulin detemir significantly lowered (7.6 +/- 0.6%, p < 0.001). In the age-group above 12 yr of age at the start of the study, the improvement of HbA1c after 12 months of treatment was less pronounced (8.0 +/- 1.2 vs. 7.6 +/- 1.0%) but still significant (p < 0.01). The risk for severe hypoglycemia was significantly decreased compared with patients attending the outpatient clinic between 1995 and 2003 (4.8/100 patient years vs. 7.6/100 patient years, p = 0.003). From the beginning to the end of the follow-up period, body mass index dropped significantly in children below 12 yr of age but no effect was observed in adolescents. CONCLUSIONS: Use of insulin detemir allows a safe nocturnal glycemic control in children and adolescents with type 1 diabetes and is associated with significantly improved HbA1c levels and fewer severe hypoglycemic events. This makes insulin detemir a most valuable new tool for the treatment of children and adolescents with type 1 diabetes.