Youths with type 1 diabetes mellitus may decide to use insulin pump therapy. Limited information describes youths’ glycemic control with insulin pump therapy. A repeated-measures design guided data collection at five points from one month before insulin pump therapy through 12 months with insulin pump therapy. The research question was, “How do youths’ hemoglobin A1c (HbA1C) values change with insulin pump therapy?” Glycemic control target was 7.6% HbA1C value. Thirty youths (9 to 18 years old) had at least 4 HbA1C values. Nineteen youths who achieved glycemic control had three different patterns during 12 months of insulin pump therapy. Eleven youths who did not achieve glycemic control had two different patterns. Multiple factors can influence a youth’s glycemic control. Uncontrolled blood glucose levels increase the individual’s risk for developing type 1 diabetes complications. Youths and health care providers need to work as a team to identify factors affecting the youth’s glycemic control and discuss changes.