**Abstract**

Olfaction is an underestimated sensory modality in terms of its predictive value as an indicator of disorders. It is a well-known phenomenon that a significant percentage of people afflicted with certain prevalent disorders causing degenerative neuropathology, progressive loss of memory and communication function, normal age-based decline of physiological functions, intellectual challenges, depressive and anxiety disorders as well as post-traumatic stress disorders, present with a range of olfactory deficits. Here, we review our understanding of these deficits and their relation to various clinical manifestations such as neurological and neuropsychiatric diseases and disorders. At the outset, we will briefly describe the olfactory pathway from olfactory sensory neurons in the nasal epithelium to the olfactory bulb and on to olfactory cortical and subcortical structures involved in olfaction such as the amygdala.

**Keywords:** aging, Alzheimer's disease, amygdala, dementia, hippocampus, limbic system, mood disorders, olfactory bulb, olfactory cortex, olfactory sensory neuron, Parkinson's disease
