Objectives: There are few methods to discern driving risks in patients with early dementia and mild cognitive impairment (MCI). We aimed to determine whether structural magnetic resonance imaging (MRI) of the hippocampusa biomarker of probable Alzheimer pathology and a measure of disease severity in those affected is linked to objective ratings of on-road driving performance in older adults with and without amnestic MCI. Methods: In all, 49 consensus-diagnosed participants from an Alzheimer's Disease Research Center (15 diagnosed with amnestic MCI and 34 demographically similar controls) underwent structural MRI and on-road driving assessments. Results: Mild atrophy of the left hippocampus was associated with less-than-optimal ratings in lane control but not with other discrete driving skills. Decrements in left hippocampal volume conferred higher risk for less-than-optimal lane control ratings in the patients with MCI (B1.63, standard error [SE] .74, Wald 4.85, P .028), but not in controls (B0.13, SE .415, Wald 0.10, P .752). The odds ratio and 95% confidence interval for below-optimal lane control in the MCI group was 4.41 (1.18-16.36), which was attenuated to 3.46 (0.88-13.60) after accounting for the contribution of left hippocampal volume. Conclusion: These findings suggest that there may be a link between hippocampal atrophy and difficulties with lane control in persons with amnestic MCI. Further study appears warranted to better discern patterns of brain atrophy in MCI and Alzheimer disease and whether these could be early markers of clinically meaningful driving risk.