All the paranasal sinuses originate embryologically from the lateral nasal wall or ethmoid air cells. This common development also determines the ability of the paranasal sinuses to function normally. Disease affecting the common drainage area of the sinus ostia, the ostiomeatal complex, also affects the function of the closely associated paranasal sinuses. Therapy directed toward any sinus without efforts to identify and correct the pathologic process of the ostiomeatal complex often leads to less-than-satisfactory results. Determination of the etiology of chronic paranasal sinus disease depends on the clinical history, endoscopic rhinoscopy, and computerized imaging. Therapy is directed toward relief of the sinus ostial obstruction and restoration of the normal mucociliary clearance. After medical therapy has failed to reverse the pathophysiology of acute or chronic paranasal sinus disease, surgical intervention may be considered.