Background: During Ramadan month Muslims neither eat or drink from down to sunset. Islam exempts some Muslims from fasting including diabetic patients. However, many diabetic patients insist on fasting without proper medical advice. Objectives: To determine the clinical effects of Ramadan fasting on diabetic patients, to identify the underlying factors of these effects and to outline recommendations for the lifestyle changes. Subjects and Methods: This follow up study recruited 284 Muslim diabetic patients from two hospitals in Qualubeya Governorate. Of these, only 200 patients completed the study. The patients were assessed by a structured questionnaire, Diabetes Symptom Checklist, anthropometric measurement and blood samples were collected to measure fasting blood glucose, cholesterol, triglyceride, High Density Lipoprotein cholesterol (HDL-c), Low Density Lipoprotein cholesterol (LDL-c) and glycated hemoglobin (HbA1c). Results: There was significant increase in DM symptoms and significant decrease in body mass index, waist-hip ratio, cholesterol, triglycerides, LDL-c and HbA1c. Complications during Ramadan fasting were associated with physical inactivity, previous DM complications, complications during Ramadan fasting in the previous year, decreased food intake, increased fluid intake and decreased/increased sugar intake during Ramadan month. Conclusion: Ramadan fasting is associated with DM complications in diabetic patients. So, management plans are recommended to minimize these complications.