There are many recent advances in insulin treatment of type 1 diabetes, however after a meal sugars are always a concern. There is a drug sitagliptin (Januvia) which is FDA approved to treat people with type 2 diabetes which helps correct their glucoses (sugars) after meals. This study is going to test whether this drug can improve the after meal sugars in people with type 1 diabetes. To test this you will be given a test mixed meal and its effects on insulin, other hormones that affect blood glucose as well as your sugar will be measured by a series of blood tests. Insulin dose will be reduced by 20-50% to prevent low blood sugars which might occur because of food staying longer in the stomach than usual or due to the suppression of a hormone called glucagon which increases blood sugar. If you qualify you will be given sitagliptin (Januvia) 3 different times in 25 mg, 50 mg and 100mg dosages. You and the researchers will not know which dose you are taking at any single visit. A total of 30 people in which some will be children aged 13- 17 and others will be adults aged 18-30 will participate. Some will have had diabetes for over a year, others will be within 3 months of having been found to have type 1 diabetes. Furthermore, only 18-30 year people who are diagnosed with type 1 diabetes for a year or more will be studied initially (4 subjects) to establish safety data before younger subjects are enrolled into the study.