In the introduction normal sinus anatomy and physiology are discussed. The epidemiology, definition, diagnosis and management of both acute and chronic rhinosinusitis are reviewed. ARS in adults is defined by the sudden onset of two or more symptoms, one of which should be nasal blockage/obstruction/congestion or nasal discharge, ±facial pain/pressure, ±reduction or loss of smell for less than 12 weeks. In children ARS is defined as a sudden onset of two or more of the following symptoms in a period during less than 12 weeks: nasal blockage/obstruction/congestion, discoloured nasal discharge or cough. ARS is self-limiting in most cases. Therefore, its management consists of symptomatic treatment with nasal decongestants, saline nasal douches and/or painkillers. For moderate or severe disease intranasal corticosteroids can be prescribed. In case of severe disease, prescribing oral corticosteroids can be considered. Antibiotic therapy should be reserved for patients with multiple symptoms of severe disease. Furthermore, possible complications of ARS are discussed, which can be categorized into orbital, intracranial or osseous.