Aim: Children under 6 yr have the highest incidence of severe hypoglycemia (SH) and the greatest likelihood of brain damage from SH. The purpose of this study is to evaluate the use of insulin glargine (Lantus (R)) in children under age 6 with type 1 diabetes (T1D). Methods: The electronic medical records were reviewed for patients under age 6 during the first 6 months of insulin glargine therapy and compared with age, sex, and duration of diabetes for matched control patients on neutral protamine Hagedorn (NPH) insulin. Data from 128 subjects (32 male pairs and 32 female pairs) were collected relating to the incidence of severe and non-severe hypoglycemic events, hemoglobin Ale (HbA1c) values, body mass index (BMI), and daily insulin dose. Additionally, parents were asked to complete a diabetes Quality of Life (QoL) survey. Results: In the 6 months before the study period, the glargine group had 16 SH events compared with three in the 6 months post-glargine. The comparison (NPH) group had seven and six SH events in their respective 6-month periods. Nighttime SH events in the glargine group decreased from 12 prestudy events to one during the study period. The average daily insulin dose in the glargine group was higher than that in the NPH group (0.8 +/- 0.2 vs. 0.7 +/- 0.2 U/kg/day; p = 0.03). The and QoL responses were not significantly different BMI HbA1c values,, between the two groups. Conclusions: SH was decreased, particularly at night (from 12 episodes to one), after the introduction of glargine in young children with T1D.