The aim of this study was to evaluate the efficacy of long-acting insulin analogue glargine (G) changing from NPH in basal-bolus therapy for Japanese children and adolescents with type 1 diabetes mellitus (DM1). Thirty patients (11 M, 19 F) with DM1 aged 13.3 ± 4.5 years were included in the study. Mean fasting blood glucose level was significantly decreased (baseline: 142.5 ± 39.3 vs 127.1 ± 24.0, 129.0 ± 29.1, 121.1 ± 26.0 mg/dl at 3, 6, 12 months, respectively, ρ <0.01), and mean HbAi c was significantly decreased (baseline: 8.06 ± 0.85 vs 7.69 ± 0.89, 7.57 ± 0.93, 7.36 ± 0.95%, at 3, 6, 12 months, respectively, ρ <0.01) after changing to G from NPH. Severe hypoglycemia rarely occurred during the study period. In conclusion, basal-bolus therapy using G resulted in improved overall glycemic control with a low risk of severe hypoglycemia in Japanese pediatric patients with DM1.