Olfactory dysfunction constitutes one of the earliest signs of Alzheimer's disease (AD) and has been shown in individuals with amnestic mild cognitive impairment (aMCI). Whether the severity of olfactory impairments in aMCI patients parallels those in AD has not been clearly established. In addition, given reports of asymmetries in neuropathological burden in early AD, functional asymmetries in olfactory performance may enhance early detection if olfactory function is assessed unirhinally. We compared AD, aMCI, and healthy participants on olfactory identification and memory assessed unirhinally. Olfactory identification was most proficient in the healthy participants and least proficient in AD, although this disparity did not depend on nostril side. Nevertheless, when only the worst nostril of each participant was included in the analysis, aMCI patients outperformed their AD counterparts. In contrast, when only the best nostril of each participant was included in the analysis--often regarded as an estimate of birhinal performance--this difference between aMCI and AD dissipated. Olfactory memory did not differ significantly across the groups, perhaps reflecting a floor effect. The findings support the hypothesis that unirhinal olfactory assessment may assist in differentiating between demented and nondemented individuals.