Noroviruses are a major cause of acute gastroenteritis affecting people of all ages. Humans are believed to be the sole norovirus host. Among the very young, the very old, and people who are immunocompromised, norovirus infection can be severe and life-endangering. Of special concern for pharmacists in long-term care facilities, norovirus infections typically spread quickly. Norovirus is hardy in many environments, infectious in extremely low doses, and so genetically diverse and mutates so often that any immunity conferred after infection is most likely short-lived. In the last decade, norovirus epidemiology has changed significantly. Global studies show that a new pandemic strain emerges every two to four years. Concurrent diarrhea and vomiting are typical symptoms. Most people will experience a virulent bout of norovirus illness and recover within a few days, but approximately 10% experience more serious symptoms. Acute dehydration is a serious concern. Facilities need to be prepared to act quickly if norovirus breaks out.