In House M.D., Dr. House’s apartment number on Baker Street was 221B.
The address is a deliberate reference to 221B Baker Street, the fictional London home of Sherlock Holmes. House was designed with several Holmes parallels, including his deductive approach, unconventional methods, drug use, musical ability, and friendship with a character analogous to Dr. Watson.
Within the series, House’s address is given as 221B Baker Street in Princeton, New Jersey. This is not the real Sherlock Holmes address in London, but an adaptation of the famous literary location for the show’s American setting.
The reference is easy to miss because the series usually focuses on hospital cases rather than House’s domestic life. It is also sometimes reported simply as “Baker Street,” but the identifying apartment designation is 221B.