An internist is a medical doctor who specializes in the care of adults. People might choose an internist as their primary doctor for regular checkups and for treating illness.

Internists can further specialize in:

• Adolescent medicine (conditions and diseases common to teenagers).
• Allergy, or immunology (immune system diseases).
• Cardiac electrophysiology (problems with the heart's electrical system).
• Cardiology (diseases and conditions of the heart and blood vessels).
• Critical care medicine (the care of people who are in an intensive care unit, or ICU).
• Endocrinology (diseases of the endocrine glands, which regulate hormones).
• Gastroenterology (diseases of the digestive system).
• Geriatric medicine (conditions and diseases in older adults).
• Hematology (diseases of the blood and blood system).
• Infectious disease (complex infections).
• Interventional cardiology (procedures to diagnose and treat heart disease).
• Nephrology (diseases of the kidney and urinary system).
• Oncology (cancer).
• Pulmonology (lung diseases such as asthma, emphysema, and pneumonia).
• Rheumatology (immune system diseases and diseases of the joints).
• Sports medicine (the treatment of injuries to the bones, muscles, joints, tendons, or ligaments that result from physical activity).

Internists can be board-certified by the Board of Internal Medicine, which is recognized by the American Board of Medical Specialties.