Studies have shown that number transcoding abilities (ie, translating numbers from one numerical code to another) are affected early in the development of Alzheimer disease (AD). However, no study has extensively explored how these abilities are affected in individuals with mild cognitive impairment (MCI).To determine the contribution that number transcoding tasks make to the identification of MCI, and to pinpoint the cognitive correlates of performance in these tasks.We compared the performance of 20 individuals with the amnestic subtype of MCI, eight individuals with AD, and 20 healthy controls on three number transcoding tasks.The results confirmed the presence of number transcoding impairment in the individuals with AD. The individuals with MCI were found to be impaired in two of the transcoding tasks; these individuals produced perseverations of the input code-the most noteworthy error type in individuals with AD. In addition, the relationship between impairment in attentional and executive functions and impairment in number transcoding was supported by the correlational analyses.This study confirmed that number transcoding abilities are impaired in individuals with MCI, although less severely than in individuals with AD. Our results provide evidence for the clinical value of including number transcoding tasks in the assessment of cognitive deficits associated with pathological aging.