Just as is the case with all medical disorders, it is knowledge of the anatomy and the systematic evaluation of the patient by physical examination (including the ENT region) that gives us the vital clues to establish the nature of an olfactory problem. At first presentation, it is vital to ascertain what kind of olfactory impairment is present: total loss of smell, partial loss, altered sensation (increased or decreased acuity) or additional unpleasant olfactory sensations. The pathological mechanisms resulting in olfactory disturbance are varied, including head injury, URTI, tumours within the anterior cranial fossa, exposure to noxious substances and infections, amongst others. Olfactory disturbance is a key feature of a number of clinical syndromes, such as Kallmann syndrome, in which hypogonadism is accompanied by anosmia, and Foster-Kennedy syndrome, in which a meningioma arising within the olfactory groove typically results in papilloedema, one-sided loss of smell plus atrophy of the optic nerve. If the cribriform plate is fractured in a head injury, there is a potential for CSF leakage from the nose and the risk of meningitis infections. Paranasal sinus endoscopy may occasion damage to the cribriform plate, which opens the way to cerebral infection. Both surgical craniotomy of the anterior base of the skull and a subarachnoid haemorrhage have the associated risk of damage to the olfactory nerves. In this chapter, the clinical assessment of olfactory disorders is discussed.