Study of repeated learning mechanisms has been limited in amnestic mild cognitive impairment, a preclinical stage of Alzheimer disease modifiable by cognitive rehabilitation. We assessed repeated contextual working memory decline as an indicator of amnestic mild cognitive impairment in a sample of 45 older adults recruited from the tertiary care setting. Results indicated that contextual working memory impairment distinguished adults with preclinical disease from those without impairment despite similar overall cognitive performance, and comparison of the indicator with standard-of-care neuropsychological measures indicated discriminant validity. Contextual working memory impairment may represent a novel predictor of Alzheimer disease conversion risk.