The clinical diagnosis of influenza can be very difficult or rather easy depending on the circumstances. It's easy when the epidemiological context is appropriate; the patient is a school kid or a teenager, and the symptoms are typical. On the other hand, it is hard when it fails to match any of the above premises, the more imformation that is missing, the more difficult it becomes. The symptomatology is correlated with age; therefore, typical clinical manifestations are only referred from 3-4 y old: rhinitis, fever with or without chills, cough, headache, joint and muscle pain and malaise. The patient often says he/she "feels sick" but his/her general condition is not at all serious. A rapid influenza diagnosis has been shown to reduce unnecessary test and antibiotics in pediatric patients and allows rational use of antivirals, early discharge from emergency departments and hospital wards, appropriate infection control measures and cohorting of infected patients. Tests that yield results in a timely manner that can influence clinical management are recommended to guide patient care. Results of testing should take into account the a priori likelihood of influenza infection based on the patient's signs and symptoms, the sensitivity and specificity of the test used, and information on circulation of influenza in the community. Failing to use the option of microbiological diagnosis when appropriate is a missed opportunity that can generate anxiety without justification, avoid unnecessarily antibiotics, omit antiviral therapy when convenient, and a teaching possibility.