What is Internal Medicine?
Internal Medicine doctors, also known as internists, are comparable to pediatricians, except that instead of treating children they treat adolescents and adults.  Just as pediatricians have specialized training in the treatment of children, so internists have specialized training in the treatment of adolescents and adults.
Internal medicine doctors cover the full spectrum of medical care for adolescents and adults, from preventive exams, colds and flu, to complex medical conditions.  Internists are sometimes referred to as the "doctor's doctor," because they are often called upon to act as consultants to other physicians to help solve puzzling diagnostic problems. 
Internists are the only primary care physicians whose training is focused solely on the medical care of adolescents and adults.  Other primary care physicians include obstretricians/gynecologists, pediatricians, and family practice doctors.  Family practice doctors are very common in rural areas where there tend to be fewer doctors with specialized training in internal medicine, pediatrics, and obstetrics/gynecology.

Because of the focused training internists have, we recommended that all adults see an internist as their primary care physician, provided that there is one available in your area.  When children reach age 13, they can start transitioning their care to a doctor of internal medicine.