Most U.S. medical students seek a categorical position for residency training in a given specialty during their final year in medical school. A "categorical" position is one which offers full residency training required for board certification in that specialty. A "preliminary" position, in contrast, is a position offering only one to two years of training generally prior to entry into advanced specialty programs. Many internal medicine and surgery training programs offer preliminary positions in addition to categorical positions. Transitional year programs are also considered preliminary year training programs.
Detailed information on 20 major fields which senior medical students can select for residency training is provided at this web site under "Choosing a Specialty." These specialties include anesthesiology, dermatology, diagnostic radiology, emergency medicine, family practice, general surgery, internal medicine, neurological surgery, neurology, obstetrics and gynecology, ophthalmology, orthopaedic surgery, otolaryngology, pathology, pediatrics, physical medicine and rehabilitation, plastic surgery, psychiatry, radiation oncology and urology.
Advanced positions, which do not commence until one to two years after the match, are in specialty programs that require completion of one or more years of preliminary training. Applicants without prior graduate medical training (i.e., U.S. seniors) may apply for these positions while also applying for preliminary positions that are compatible with their plans. The following specialties offer advanced positions (some of these may also have programs which offer categorical positions): urology, ophthalmology, dermatology, diagnostic radiology, radiation oncology, physical medicine and rehabilitation, neurology, psychiatry and anesthesiology.