We compared 7 mildly affected Huntington's disease (HD) patients to 7 age- and education-matched healthy controls (NC) on an odor detection test, the California Odor Learning Test, and the California Verbal Learning Test. Results demonstrated that odor detection sensitivity, but not group membership, accounted for significant variance in total olfactory learning. Both groups learned fewer items in the olfactory modality compared to the verbal modality, but retained a similar amount following a delay. No group differences were demonstrated for verbal recognition discriminability, but the HD group demonstrated significantly impaired odor recognition discriminability. Finally, odor detection provided excellent classification sensitivity and specificity between the patients and controls, suggesting that olfactory testing may provide a sensitive measure of the early disease process in HD. (JINS, 1999, 5, 609–615.)