What was House’s medical specialty in House M.D.?

House’s medical specialty in House M.D. is diagnostic medicine.

Gregory House heads the Department of Diagnostic Medicine at Princeton-Plainsboro Teaching Hospital. His team handles patients whose symptoms do not fit an obvious diagnosis or whose earlier treatments have failed.

Diagnostic medicine is presented in the series as a broad, puzzle-solving discipline rather than a routine ward specialty. House draws on knowledge from many medical fields, orders tests, and revises hypotheses as new evidence appears.

The character is also identified as a specialist in nephrology and infectious disease. Those are important parts of his professional background, but they are not the department he leads in the show. The canonical answer to the question about his hospital role is therefore diagnostic medicine.