Background: Despite reports of gross motor problems in mild cognitive impairment (MCI) and Alzheimer’s disease (AD), fine motor function has been relatively understudied.

Objective: We examined if finger tapping is affected in AD, related to AD biomarkers, and able to classify MCI or AD. Methods: Forty-seven cognitively normal, 27 amnestic MCI, and 26 AD subjects completed unimanual and bimanual computerized tapping tests. We tested 1) group differences in tapping with permutation models; 2) associations between tapping and biomarkers (PET amyloid-, hippocampal volume, and APOE 4 alleles) with linear regression; and 3) the predictive value of tapping for group classification using machine learning. Results: AD subjects had slower reaction time and larger speed variability than controls during all tapping conditions, except for dual tapping. MCI subjects performed worse than controls on reaction time and speed variability for dual and nondominant hand tapping. Tapping speed and variability were related to hippocampal volume, but not to amyloid-deposition or APOE 4 alleles. Random forest classification (overall accuracy= 70%) discriminated control and AD subjects, but poorly discriminated MCI from controls or AD.