Only a few studies have been conducted to determine the historical background of obesity, and even fewer have focused on specific writers who have made great contributions on the subject. Galen was among the first to establish scientific methods to describe and treat morbid obesity, and a presentation of his ideas is important because of the influence he has exerted even up to modern times. The methodology of the current research was based on detailed study of Galen's treatises, which concern the nature of obesity, the etiology, the consequences, and the treatment, often in comparison to the writings of other writers from the Hippocratic period up to recent years. Galen stated that obesity results from the surplus of "bad humors" in the body and specifically from a surplus of blood. He specifically described patients' conditions, both physiologic and practical; he presented side effects; and he introduced methods of treatment that are used even today. Galen also described an illness he called polisarkia, which today we call morbid obesity. According to Galen's views, we can identify morbid obesity under the description of polisarkia. Galenic physiology and pathology have been proved wrong and have been set aside. Nevertheless, he proposed some treatments for obesity such as diet, exercise, and medications that are still valuable and are nearly the same as what is advocated today.