OBJECTIVE: This study was performed to determine the effects of the Diabetes Control and Complications Trial (DCCT) report in 1993 and the introduction of Lispro (Humalog) insulin in 1996 on glycemic control and on the number of severe hypoglycemic episodes in type 1 diabetic patients of various ages. RESEARCH DESIGN AND METHODS: Diabetes care parameters and HbA1c data from 884 subjects with type 1 diabetes were entered into our database at the time of clinic visits from 1993 through 1998. In addition, a questionnaire was sent to all patients to validate the number of insulin injections per day, the incidence of severe hypoglycemic episodes (as defined by the DCCT), and the use of Humalog insulin. Data were divided into four age-groups: < 5, 5-12, 13-18, and > 18 years of age. RESULTS: Longitudinal HbA1c levels declined significantly after the DCCT report in 1993-1996 (P < 0.001), but the number of severe hypoglycemic events increased (P < 0.001). A second decline in HbA1c levels was observed after the introduction of Humalog insulin in 1996 (P < 0.001). However, severe hypoglycemic episodes did not change (P = 0.26). CONCLUSIONS: Administration of Humalog resulted in an additional reduction in HbA1c levels beyond the reduction in HbA1c values after the DCCT report. In contrast to the increase in severe hypoglycemic events after the DCCT results, the number of severe hypoglycemic episodes did not increase after the introduction of Humalog, despite a further decrease in HbA1c values.