We investigated the percentage of total basal insulin dose to total daily insulin dose (%TBD) among Japanese youth of different ages with type 1 diabetes. The study enrolled 69 patients with type 1 diabetes who were treated with multiple daily injections of insulin. The participants were divided into the following age groups: group A, 0 to <10 years (n = 18); group B, 10 to <20 years (n = 31) and group C, 20 to <25 years (n = 20). We found no difference in the sex ratio, body mass index, and glycated hemoglobin and 2-h postprandial C-peptide levels among the three groups. Participants assigned to group B had a significantly higher percentage of total daily insulin dose than those in group A and group C (49.7 ± 10.4% vs 38.5 ± 13.7% and 38.3 ± 8.2%, P = 0.0005). In conclusion, the basal insulin requirements of Japanese youth with type 1 diabetes might have an age effect that is associated with puberty.