It is widely accepted that regular physical exercise helps diabetic patients control blood glucose, reduce cardiovascular risk factors, and prevent other related complications. In spite of the undoubted benefits of regular physical exercise, diabetic patients with chronic complications should be aware of potential hazards of practicing exercise. To avoid some harmful consequences of acute exercise, it is necessary to adopt a vigilant attitude with these risk patients and to carefully adjust type and intensity of exercise to the individual situation. This article intends to summarize and analyze the current literature concerning the preventive and therapeutic effects of regular exercise in diabetic patients, pointing out its physiological influence on blood glucose regulation, and to analyze the potential risks of acute physical exercise and the precautions given to patients with a variety of complications.