Sitagliptin will be given in three different doses to T1DM subjects within 3 months of diagnosis and also in a group of subjects > 1 year of their diagnosis. A paired crossover design study aims to establish an effective glucose-lowering dose that will additionally minimize side effects. Furthermore, only 18-30 year old subjects who are diagnosed with T1DM for a year or more will be studied initially (4 subjects) to establish safety data before younger subjects are recruited into the study. The data will be un-blinded after the completion of the first two adult subjects in order to analyze preliminary data and also to reapply for funding. Data Safety Monitoring Board will meet before the initiation of the study and before children are enrolled into the study. The safety data after the meeting will be submitted to the IRB for review.