Vaccination is the primary measure for preventing morbidity and mortality from influenza. During the influenza season, family physicians must distinguish influenza from the common cold and other flu-like illnesses. Signs and symptoms of influenza include abrupt onset of fever, severe myalgias, anorexia, sore throat, headache, cough, and malaise. Clinical diagnosis can be difficult or nonspecific when patients have other symptoms (e.g., stuffy nose, sneezing, cough, sore throat) that can be caused by various respiratory viruses or bacterial pathogens. Family physicians can improve diagnostic accuracy by being aware of the epidemiology of influenza. During outbreaks of influenza, commercially available rapid assays can be used to identify type A and B viruses. On average, rapid in-office tests are more than 70 percent sensitive and 90 percent specific for viral antigens. The assays vary in complexity, specificity, sensitivity, time to obtain results, specimen analyzed, and cost. The results of rapid viral tests can guide treatment decisions.