The etymology of the term internal medicine in English is rooted in the German term Innere Medizin from the 19th century.^[1] Internal medicine was initially characterized by determination of the underlying “internal” or pathological causes of symptoms and syndromes by use of laboratory investigations in addition to bedside clinical assessment of patients. In contrast, physicians in previous generations, such as the 17th-century physician Thomas Sydenham, who is known as the father of English medicine or “the English Hippocrates“, had developed nosology (the study of diseases) via the clinical approach of diagnosis and management, by careful bedside study of the natural history of diseases and their treatment.^[2] Sydenham eschewed dissection of corpses and scrutiny of the internal workings of the body, for considering the internal mechanisms and causes of symptoms.^[3] It was thus subsequent to the 17th century that there was a rise in anatomical pathology and laboratory studies, with Giovanni Battista Morgagni, an Italian anatomist of the 18th century, being considered the father of anatomical pathology.^[4] Laboratory investigations became increasingly significant, with contribution of doctors including German physician and bacteriologist Robert Koch in the 19th century.^[5] The 19th century saw the rise of internal medicine that combined the clinical approach with use of investigations.^[6] Many early-20th-century American physicians studied medicine in Germany and brought this medical field to the United States. Thus, the name “internal medicine” was adopted in imitation of the existing German term.^[1]

Historically, some of the oldest traces of internal medicine can be traced from ancient India and ancient China.^[7] Earliest texts about internal medicine are the Ayurvedic anthologies of Charaka.^[8]