Research has associated olfactory loss, or anosmia, with cognitive decline, mild cognitive impairment (MCI) or Alzheimer’s disease (AD). It may also be a marker for Lewy body and vascular dementia. Early detection can help prevent or delay these diseases, and olfactory impairment may be an important clinical marker and predictor of these conditions. There is a suggested association between olfactory impairment, incidental MCI and progression from aMCI to AD dementia, and studies link olfactory impairment with cognitive impairment in late life. The olfactory bulb is thought to be involved because smell loss occurs only in neurodegenerative conditions where there is olfactory pathology, such as Alzheimer’s Disease and Parkinson’s disease. Neurofibrillary tangles, features of AD, have been found in the olfactory bulb and tracts before the onset of symptoms, suggesting that olfactory deficits may be early markers of the disease.