Neuropathological research consistently revealed that the olfactory bulb and tract (OBT) is subjected to degenerative processes in Alzheimer's disease (AD). In the present study, we assessed OBT volumes in individuals with mild cognitive impairment (MCI), in patients with probable AD, and in healthy comparison subjects using high-resolution magnetic resonance imaging. In both MCI and AD patients OBT volumes were significantly lower compared to controls with atrophy being most prominent in the AD group. In the patient group, lower mean OBT volumes were associated with a decreased gray matter density in the MTL bilaterally. Further, OBT volumes in patients were significantly correlated with cognitive performance. Our findings suggest the OBT volume as a potentially useful marker of AD and MCI related neurodegeneration.