To determine the effect of insulin glargine on glycemic control in pediatric type 1 and 2 diabetes, a retrospective repeated-measure analysis of variance was performed of hemoglobin A1C (HbA1C), frequency of hypoglycemia and hyperglycemia, mean blood glucose, body mass index (BMI), and daily weight-adjusted insulin dosage before and after institution of glargine therapy in 72 children and adolescents with diabetes. At glargine start, age range was 1.2-19.6 years, mean age was 12.5 +/- 4.6 years, BMI was 22.48 +/- 6.3 kg/m(2), and mean HbA1C was 9.7 +/- 1.9%. Mean duration of diabetes was 3.58 years, and mean baseline insulin dose was 0.93 U/kg/day. Gender breakdown was 60% female, and the majority (83%) had type 1 diabetes. Average HbA1C decreased from 9.5% pre-glargine to 8.6% post-glargine (p < 0.001). HbA1C decrease was significant in both types of diabetes without a concomitant increase in frequency of hypoglycemia, BMI, or weight-adjusted insulin dose. Hypoglycemia decreased significantly in type 1 diabetes. Thus, glargine therapy may decrease HbA1C and frequency of hypoglycemia in toddlers, children, and adolescents with diabetes, without an increase in BMI or insulin requirements.