Internal medicine is a medical specialty that deals with the diagnosis and medical, as opposed to surgical, treatment of diseases of adults. It is broadly identical with the practice of the physician, as opposed to that of the surgeon. Internal medicine, which deals with the entire patient rather than a particular organ system, is in effect the parent of other medical specialties such as cardiology, dermatology, and gastroenterology. An advanced practitioner of internal medicine is called an internist in the United States and many other countries.

Internal Medicine covers a wide range of conditions affecting the internal organs of the body - the heart, the lungs, the liver and gastro-intestinal tract, the kidneys and urinary tract, the brain, spinal column, nerves, muscles and joints. Although some diseases specifically affect individual organs, the majority of common diseases - arteriosclerosis, diabetes, high blood pressure and cancer may affect many internal organs of the body. The internist must then be trained to recognize and manage a broad range of diseases and, with the aging population, many patients with chronic and multiple disorders.