MCI is an intermediate cognitive state between normal aging and dementia. Most MCI patients transition to AD, but some remain stable and others improve. Hippocampal volume measures are sensitive to early brain change, therefore hippocampal atrophy correlates strongly with pathological staging and cognitive decline, and predates conversion of MCI to AD in the old. MRI-based volumetric measurements of hippocampus are being used clinically with increasing frequency, because of it accurately depicts the structural-functional relationships between memory loss and hippocampal damage across the spectrum from MCI to AD. Smaller hippocampi and specifically CA1 and subicular involvement are associated with increased risk for conversion from MCI to AD and these quantitative, dynamic visualizations of hippocampal atrophy rates in MCI and AD may provide a promising measure to track AD progression in drug trials.