In encounters between general practitioners (GPs) and patients with medically unexplained symptoms (MUS), the negotiation of the sick role is a social process. In this process, GPs not only use traditional biomedical diagnostic tools but also rely on their own opinions and evaluations of a patient's particular circumstances in deciding whether that patient is legitimately sick. The doctor is thus a gatekeeper of legitimacy. This article presents results from a qualitative interview study conducted in Denmark with GPs concerning their approach to patients with MUS. We employ a symbolic interaction approach that pays special attention to the external validation of the sick role, making GPs' accounts of such patients particularly relevant. One of the article's main findings is that GPs' criteria for judging the legitimacy of claims by those patients that present with MUS are influenced by the extent to which GPs are able to constitute these patients as people with social problems and problematic personality traits.