1. Surgical or internal medicine
2. Age range of patients
3. Diagnostic or therapeutic
4. Organ-based or technique-based
- Throughout history, the most important has been the division into surgical and internal medicine specialties. The surgical specialties are the specialties in which an important part of diagnosis and treatment is achieved through major surgical techniques.
- The internal medicine specialties are the specialties in which the main diagnosis and treatment is never major surgery. In some countries Anesthesiology is classified as a surgical discipline, since it is vital in the surgical process, though anesthesiologists never perform major surgery themselves.
- Many specialties are organ-based. Many symptoms and diseases come from a particular organ. Others are based mainly around a set of techniques, such as radiology, which was originally based around X-rays.
- The age range of patients seen by any given specialist can be quite variable. Paediatricians handle most complaints and diseases in children that do not require surgery, and there are several subspecialties (formally or informally) in paediatrics that mimic the organ-based specialties in adults.
- Paediatric surgery may or may not be a separate specialty that handles some kinds of surgical complaints in children.
- A further subdivision is the diagnostic versus therapeutic specialties. While the diagnostic process is of great importance in all specialties, some specialists perform mainly or only diagnostic examinations, such as pathology, clinical neurophysiology, and radiology.
- This line is becoming somewhat blurred withinterventional radiology, an evolving field that uses image expertise to perform minimally invasive procedures.