Definitions differ depending on the classification system, for example a temporal or symptom based approach. The Task Force on Acute Rhinosinusitis in 1997 (1) used a temporal based approach to define acute rhinosinusitis as disease that had been present for four weeks or less, subacute as presence of disease between 4-12 weeks and chronic as 12 weeks. Recurrent acute disease was defined as occurring several times a year but improving between episodes, thus not qualifying as chronic rhinosinusitis.

Rhinosinusitis can also be defined according to signs and symptoms. The Task Force developed a method of diagnosing rhinosinusitis according to the presence of two major factors, or one major and two minor factors. Major factors include facial pain in the area of the sinuses, nasal obstruction, nasal congestion, purulent drainage, decreased smell and relatively new onset of cough. The minor factors are less specific and include headache, fever, halitosis, fatigue, dental pain and other signs or symptoms.