Patients who have lost the sense of smell usually come to a doctor on their own, reporting loss of the sense of taste. Inflammation (often due to allergy), viral infection, and head trauma are common causes of olfactory disturbance. History taking may provide clues to these and other problems (eg, toxin exposure, congenital dysosmia). Workup should not begin until a standardized test has been given that established impairment of the sense of smell. The only truly reversible cause is inflammation, which is confirmed when smell returns after a course of corticosteroid. Sinus computed tomography is necessary to view the olfactory cleft; lack of obstruction indicates that smell impairment is nonreversible. Patients deserve an explanation for their disorder and a prognosis. If restoration of their sense of smell is unlikely, patients should be cautioned to take steps to ensure safety in regard to such dangers as gas leaks, smoke, and spoiled foods.