Chronic rhinosinusitis is a multifactorial disease defined as inflammation of the nasal cavity and paranasal sinuses with a history of at least 12 weeks in duration. The major symptoms include facial pressure or pain, nasal obstruction, discharge or purulence, and hyposmia or anosmia. The minor symptoms include fever, halitosis, fatigue, and dental pain. Microorganisms play a significant role in the persistence and origination of the inflammatory process, although the exact role of these organisms in the pathogenesis of chronic rhinosinusitis is unclear. The clinical diagnosis relies heavily on the patient history and physical examination, which may include nasal endoscopy and computed tomography. Diagnostic techniques are here reviewed.