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. To become gastroenterologists, they complete three years of additional study after that. Then they receive a special certification. This certification designates them as experts in gastrointestinal diseases and conditions. It also qualifies them to perform certain exams and procedures that general physicians don’t, and to interpret the results.