ObjectiveTo study BMI changes and glycemic control in children and adolescents during the first 5 years following diagnosis of type 1 diabetes.Research design and methodsThe 295 children and adolescents (<18 years) diagnosed with type 1 diabetes started on multiple injection treatment and were followed during the first 5 years of treatment with respect to glycemic control and weight change. Growth curves preceding the onset of diabetes were obtained from the school health services and child care centers. BMI was recalculated into BMI SD scores (BMISDS).ResultsPrior to the onset of diabetes, the BMISDS was 0.46 ± 1.24 (mean ± SD), which decreased to −0.61 ± 1.36 (p < 0.001) at presentation. At 1 year, BMISDS was 0.59 ± 0.99 (p > 0.05) and increased to 0.80 ± 1.03 at 5 years; 0.97 ± 0.93 in females versus 0.68 ± 1.08 in males (p < 0.001). BMISDS at 1 year and 5 years were directly proportional to and highly predicted by BMISDS prior to the onset of type 1 diabetes, (r = 0.76; p < 0.001) vs. (r = 0.58; p < 0.001). HbA1c at 1 year was 50 ± 10 mmol/mol, which increased to 58 ± 12 mmol/mol (p < 0.001) at 5 years; females had HbA1c 60 ± 14 mmol/mol versus males 56 ± 11 mmol/mol (r = 0.35, p < 0.001). There was a correlation, irrespective of gender, between HbA1c and BMISDS at 1 year (r = 0.18, p < 0.003), but not at 5 years (r = 0.036, (p > 0.5).ConclusionDuring the first 5 years of treatment of type 1 diabetes in children and adolescents it is possible to achieve good glycemic control without excess weight gain.