A retail clinic is a category of walk-in clinic located in retail stores, supermarkets and pharmacies that treat uncomplicated minor illnesses and provide preventative health care services. They are sometimes called "retail-based clinics," "convenient care clinics," or "nurse-in-a-box." Retail clinics in the United States are usually staffed by physician assistants (PAs) or nurse practitioners (NPs) and do not necessarily have a physician physically available onsite.[1] Some, however, are staffed by physicians.