Exercise is becoming more widely used to prevent and treat the diseases that are most prevalent in the United States: coronary artery disease, stroke, hypertension, diabetes, arthritis, osteoporosis, dyslipidemia, obesity, depression, cancer, and chronic obstructive pulmonary disease. However, physicians need more training in how to make best use of this powerful therapy. Physicians can successfully encourage activity by giving patients a written exercise prescription along with printed advice on how to design a safe, enjoyable routine.