Age-related alterations in the ability to smell are well documented. For example, more than three-fourths of individuals over the age of 80 have major difficulty detecting and identifying odors. Furthermore, olfactory dysfunction is among the first signs of Alzheimer's disease (AD). Indeed, the olfactory pathways of patients with AD evidence disproportionate numbers of neuritic plaques and neurofibrillary tangles relative to other sensory pathways, suggesting that the olfactory system may be the site of first involvement of the AD process. In this article, the literature related to age- and AD-related alterations in olfactory perception has been briefly reviewed, and several current hypotheses regarding the physiologic basis for these changes discussed.