Accurate diagnosis of patients presenting with rhinosinusitis symptoms is the key to effective disease management. A multidisciplinary task force of expert physicians and related specialists achieved consensus on a standard definition of rhinosinusitis for clinical care and research settings in Taiwan. Rhinosinusitis may be defined as an inflammatory process involving the mucous membranes of the paranasal sinuses. Because this condition commonly involves the nasal mucosa as well, some clinicians prefer to use the term rhinosinusitis in stead of sinusitis. The definition establishes a consistent, uniform baseline for diagnosis in patients and may facilitate development of a proper treatment plan.