Internal Medicine is the branch of medicine which includes what most people consider “adult” medicine. Doctors who specialize in internal medicine have intensive training in many disease processes, and there is a strong bias toward hospitalized patients. Many doctors who specialize in internal medicine go on to specialize in a branch of internal medicine such as cardiology (heart), endocrinology (diabetes, thyroid, etc.), pulmonary (lungs), etc.
Family Practitioners spend at least a third of their residency dealing with internal medicine, mostly doing rotations on various hospital services (cardiology, general internal medicine, etc.). Internal medicine is also an integral part of the re-certification examination required every 7 years to maintain board certification.