A gastroenterologist is a medical doctor who specializes in conditions affecting your digestive system. Gastroenterologists begin as general physicians. They complete three years of medical residency after medical school, treating all kinds of diseases and conditions. They treat and diagnose conditions and issues that can impact or concern the gastrointestinal tract and liver. They assess the structure of the patient's digestive tract and are experts in digestive tract diseases, including polyps, peptic ulcer disease, or pancreatitis.