The human sense of smell generally fails in one of three ways. One is an intensity reduction resulting in decreased olfactory sensitivity (hyposmia or anosmia). The other two are quality changes with a distoration of the perceived odour. One type of distortion occurs when inhaled odorant do not have same" smell" or "odour" as remembered (troposmia, "to twist or turn the sense of smell"). The other type of distortion is the perception of an odour (usually unpleasant) when there is no odour in the environment (phantosmia, hallucination). These distortions are usually much more disruptive to a persons life than a simple loss, because they are repeatedly being reminded by the problem. In order to reach a proper diagnosis, the clinician should follow the sequence of detailed history taking, a thorough physical examination (including ENT and neurological assessment) and additional investigations including subjective and objective measures. Treatment of olfactory disorders differs according to the type of this disorder whether it is olfactory loss or olfactory distortion. Treatment includes both medical and surgical measures. The medical therapy for olfactory loss includes corticosteroids (local or systemic), antihistamines, antileukotrienes, antifungal therapy, saline lavage, antibiotics (e.g., roxithromycin, minocycline), theophylline, zinc sulphate, vitamin A and caroverine.