Background and Aims: Fasting during the holy month of Ramadan is an obligatory duty for all healthy adult Muslims. Fasting can be a major challenge for adolescents with type 1 diabetes mellitus (T1DM) as they have to keep good glycemic control to avoid complications. Limited data was published regarding the safety of fasting Ramadan in adolescent patients with T1DM. We have therefore conducted this study addressing the question “Can adolescents with T1DM fast safely during the Holy month of Ramadan, without getting significant hypo/hyperglycemia?” Patients and Methods: This is an observational, prospective, single center study, conducted during Ramadan 2013. Twenty-three patients were observed (7 males, 16 females). Median age was 14 years. All of them had T1DM, and were planning to observe the fast during Ramadan. They were provided with dairies to be filled by the parents or the adolescents themselves (with parental supervision), indicating the days they fasted/didn't fast, and the reasons for not fasting e.g. hypoglycemia, hyperglycemia, menstrual period, sickness or other reasons. Patients were also asked to record the blood glucose readings and their insulin doses on daily basis. They were asked to bring their folders back to the Diabetic clinic after Ramadan. Outcome measures obtained included the percentages of the days fasted/not-fasted, the reasons for not fasting, HbA1c changes, and a comparison between patients on multiple daily injections and those on insulin pump. Moreover, we studied the relationship between the number of days not-fasted due to diabetes related issues and the HbA1c before Ramadan. Results: Patients were able to fast 79.9% of the total days eligible for fasting, while 20.1% of the days were not fasted due to either hypoglycemia (29.1%), hyperglycemia (19.4%) or other reasons (51.5%). None of the patients developed severe hypoglycemia or diabetic ketoacidosis. There was a mild increment in mean HbA1c after Ramadan (from 8.3% to 8.5%). The patients on insulin pump tended to fast more days than those taking multiple daily injections (82.8% versus 77.3% out of the total eligible days). Patients who had able to fast more days without diabetes related problems tended to have had a marginally better glycemic control before Ramadan (8.3% versus 8.7%). Conclusions: Adolescent patients with T1DM wishing to fast during the holy month of Ramadan may contemplate doing this under medical supervision. The use of insulin pump therapy may help patients to fast more easily and have better control. Adequate education and good glycemic control prior to Ramadan is associated with better outcome.