OBJECTIVE To study body mass index (BMI) changes and metabolic control in children and adolescents during the first year following the diagnosis of type 1 diabetes. RESEARCH DESIGN AND METHODS 200 children and adolescents (<18 years) diagnosed with type 1 diabetes, started on multiple injection treatment and followed up for 1 year were studied with respect to metabolic control and weight change. Growth curves preceding the onset of diabetes were procured from the school health services. BMI was recalculated into BMI SD scores (BMISDS). RESULTS Glycated hemoglobin (HbA1c) at 1 year was 6.7±1.3% (50±10 mmol/mol). HbA1c was positively correlated with daily insulin dose (R(2)=0.13; p<0.001), negatively correlated with age (R(2)=0.03; p<0.05) but not related to gender, BMISDS at 1 year, HbA1c at presentation, or ketoacidosis at presentation. Prior to the onset of diabetes, BMISDS was 0.41±1.20 and decreased to -0.63±1.25 at presentation. BMISDS at 1 year was 0.54±0.97 and not different from the premorbid value (p>0.05). In a multiple regression analysis, BMISDS at 1 year was directly proportional to and highly predicted by BMISDS prior to onset of diabetes (R(2)=0.57; p<0.001). BMISDS at 1 year was also inversely correlated with age (R(2)=0.03; p<0.001) but could not be predicted by gender, daily insulin dose, HbA1c at 1 year, HbA1c at presentation, or by ketoacidosis at presentation. CONCLUSIONS During the first year of treatment of type 1 diabetes in children and adolescents, it is possible to achieve good metabolic control without excess weight gain.