There are more than 40 types of doctors in the United States, spanning primary care, surgical specialties, mental health, and dozens of subspecialties focused on specific organs or patient populations. The American Board of Medical Specialties recognizes 24 major specialty boards, and many of those branch into further subspecialties, bringing the total number of distinct physician types well above that number. Here’s how the landscape breaks down.
Primary Care Doctors
For most people, a primary care doctor is the first point of contact with the healthcare system. These physicians handle routine checkups, manage chronic conditions like diabetes or high blood pressure, and refer you to specialists when needed. Three types of doctors fill this role:
- Family medicine doctors treat patients of all ages, from newborns to older adults. They handle the broadest range of conditions in outpatient settings.
- Internal medicine doctors (internists) focus on adults. They often develop long-term relationships with patients and manage complex medical histories over the course of a person’s entire adult life. Some internists work exclusively in hospitals, where they’re called hospitalists, treating patients on a short-term basis during inpatient stays.
- Pediatricians specialize in infants, children, and adolescents. Beyond general wellness, they monitor developmental milestones and childhood-specific conditions.
Primary care residencies typically take three years after medical school.
Internal Medicine Subspecialties
Internal medicine is one of the broadest fields in medicine because it branches into so many organ-specific subspecialties. After completing an internal medicine residency, doctors can pursue additional fellowship training (usually two to three more years) to become:
- Cardiologists: heart and blood vessel conditions
- Gastroenterologists: digestive system, liver, and gallbladder
- Pulmonologists: lungs and respiratory system
- Nephrologists: kidneys
- Endocrinologists: hormones, diabetes, and metabolism
- Rheumatologists: joints and autoimmune conditions like lupus or rheumatoid arthritis
- Oncologists: cancer diagnosis and treatment
- Hematologists: blood disorders
- Infectious disease specialists: complex bacterial, viral, and fungal infections
Some of these branch even further. Cardiology alone has four additional subspecialties, including heart failure and transplant cardiology, and interventional cardiology for procedures like stenting.
Surgical Specialists
The American College of Surgeons recognizes 14 surgical specialties. General surgeons handle a wide range of operations involving the abdomen, skin, and soft tissues. Beyond that, surgeons specialize by body region or patient population:
- Orthopedic surgeons: bones, joints, ligaments, and tendons
- Neurosurgeons: brain and spinal cord (residency takes seven years, the longest of any specialty)
- Cardiothoracic surgeons: heart and chest
- Vascular surgeons: blood vessels outside the heart and brain
- Urologists: urinary tract and male reproductive system
- Plastic surgeons: reconstructive and cosmetic procedures
- Colon and rectal surgeons: lower digestive tract
- Pediatric surgeons: operations on children
Surgical residencies are longer than most medical specialties, ranging from five to seven years after medical school. Some, like cardiothoracic surgery, require a general surgery residency first followed by additional fellowship years.
OB-GYNs and Women’s Health
Obstetricians and gynecologists (OB-GYNs) manage pregnancy, childbirth, and reproductive health. Many function as a woman’s primary doctor for annual exams and preventive care. Within this field, gynecologic oncologists specialize in cancers of the reproductive system, and maternal-fetal medicine specialists handle high-risk pregnancies.
Mental Health Doctors
Psychiatrists are medical doctors who diagnose and treat mental health conditions through therapy, medication, or a combination of both. They complete four years of medical school followed by a four-year psychiatry residency, totaling eight to ten years of postgraduate training. Because they hold an MD or DO, psychiatrists can prescribe medications and perform medical procedures related to mental health.
Psychologists hold a doctoral degree in psychology (PhD or PsyD) rather than a medical degree. Their training takes five to seven years of graduate study plus one to two years of clinical training. They provide therapy and psychological testing but cannot prescribe medications in most states. If you’re unsure which to see, the key distinction is whether medication management is likely to be part of your treatment.
Pediatric Subspecialties
Children aren’t just small adults. Their bodies and diseases behave differently, which is why nearly every major adult specialty has a pediatric counterpart. The Council of Pediatric Subspecialties lists close to 20 distinct fields, including pediatric cardiology, pediatric neurology, neonatology (care of newborns, especially premature or critically ill babies), and developmental and behavioral pediatrics for children with conditions like autism or ADHD. Pediatric hematology-oncology combines blood disorders and cancer care into a single subspecialty because the two overlap heavily in children.
Other Specialists You May Encounter
Several specialties don’t fit neatly into the categories above but are ones you’re likely to be referred to at some point:
- Dermatologists: skin, hair, and nail conditions
- Ophthalmologists: eye diseases and surgery (distinct from optometrists, who primarily handle vision correction)
- Otolaryngologists (ENTs): ear, nose, and throat
- Anesthesiologists: pain management and sedation during surgery
- Radiologists: medical imaging interpretation (X-rays, MRIs, CT scans)
- Pathologists: lab analysis of tissue and blood samples to diagnose disease
- Emergency medicine doctors: acute injuries and illnesses in the ER
- Physical medicine and rehabilitation doctors (physiatrists): recovery from injuries, strokes, or surgeries without surgery
- Allergists/immunologists: allergies, asthma, and immune system disorders
- Preventive medicine doctors: population health, occupational health, and disease prevention
MD vs. DO
You’ll see two types of medical degrees on a doctor’s credentials: MD (Doctor of Medicine) and DO (Doctor of Osteopathic Medicine). Both complete four years of medical school, pass licensing exams, and train in the same residency programs. The practical differences are small. DO programs historically emphasize a holistic, patient-centered approach and include training in osteopathic manipulative treatment, a set of hands-on techniques using stretching, gentle pressure, and resistance to diagnose and treat musculoskeletal problems. Both MDs and DOs can practice in any specialty and prescribe medications.
Other Professionals With “Doctor” Titles
Not every healthcare provider called “doctor” attended medical school. Several professions earn doctoral-level degrees and require state licensure but have a more focused scope of practice:
- Dentists (DDS or DMD): teeth, gums, and oral health
- Podiatrists (DPM): feet and ankles
- Optometrists (OD): vision exams and corrective lenses (not eye surgery)
- Chiropractors (DC): spinal alignment and musculoskeletal issues
- Clinical psychologists (PhD or PsyD): therapy and psychological assessment
- Pharmacists (PharmD): medication management and drug interactions
These practitioners play important roles in healthcare, but their training and authority differ significantly from physicians. When a condition requires medical diagnosis, prescription drugs, or surgery, an MD or DO is typically the provider you’ll need.
How Doctors Get Certified
Becoming board certified requires four years of undergraduate education, four years of medical school, and three to seven years of residency depending on the specialty. After residency, doctors must obtain an unrestricted medical license and pass a specialty-specific exam administered by one of the 24 ABMS member boards. Subspecialists go further, completing additional fellowship training and passing a second board exam in their narrower field. When you see “board certified” on a doctor’s profile, it means they’ve cleared every one of these hurdles in their specific area of medicine.