St. Sebastian's Hospital is a fictional hospital in the Princeton area. It has appeared or been mentioned in several episodes. It's probably the third biggest hospital in the area after Princeton General and Princeton-Plainsboro Teaching Hospital. St. Sebastian's connection to the medical profession is as the patron saint of plagues (specifically, deliverance from them).
In Deception, Anica Jovanovich goes to St. Sebastian's after she's successfully treated at Princeton-Plainsboro in order to feed her Munchausen syndrome.
In Merry Little Christmas, after House has his Vicodin cut off, he goes to the clinic at St. Sebastian's in order to try to score narcotics.
In The Softer Side, after House quits because Cuddy won't let him use methadone, he gets an interview at St. Sebastian's to try to convince them to open up a diagnostics department.