What was Dr. House's department called in House M.D.?

Dr. House's department in House M.D. was called Diagnostic Medicine.

House led a specialized team that handled patients with unusual or unexplained illnesses, especially cases that other hospital departments had failed to solve. The department's work formed the narrative engine of the series: each episode usually presented a medical mystery followed by testing, competing hypotheses, and a final diagnosis.

Diagnostic medicine is a real area of medical practice, although the show's rapid, team-based investigations are highly dramatized. In real hospitals, difficult cases may involve internists, infectious-disease physicians, pathologists, radiologists, and many other specialists.

House himself had training in both infectious disease and nephrology, but his role at Princeton-Plainsboro was as head of Diagnostic Medicine. That distinction matters because his personal specialties were not the same as the name of his hospital department.