I'm not a nurse, so I can't speak with nurse-specific experience, but I am the hiring manager for a dept within a medical school. ALWAYS err on the side of dressing up. Although it's terribly inconvenient to have to gather an outfit together that you may not already own (and may not wear again), as the commercial goes, "You never get a second chance to make a first impression". "Dressing up" shows a level of commitment and professionalism, and no justification should be used to slide by with something more casual. A professional outfit doesn't have to be expensive. My last "interview outfit" cost me maybe $60 brand new from either Burlington Coat Factory or TJ Maxx (including shoes). YOu can get away with spending less at consignment or thrift stores, as mentioned above. Good luck with your interview and let us know how it went!