Objective: To investigate financial skill decline longitudinally in patients with mild cognitive impairment due to an etiology of Alzheimer's disease (MCI). Method: Study participants were cognitively normal older adults (n = 82) and patients with MCI (n = 91) who completed ADRC consensus conference to establish diagnosis. Participants completed up to seven annual assessments using a standardized measure of financial skills (FCI). Scores were calculated for 9 FCI domains and 3 global scores. Mean changes in FCI variables were examined across groups using mixed-model repeated measures analysis adjusted for baseline age and follow-up duration. Results: At baseline, controls performed better than MCI patients across all FCI global and seven domain scores. Group x Time interaction effects (p < .02) were found for all global scores and all domains except Cash Transactions (p < .06). The largest interaction effects were observed for complex domains of Financial Conceptual Knowledge, Checkbook Management, Bank Statement Management, and Bill Payment (all p < .0001). Annualized decline in MCI global scores, calculated in relation to control performance, was 11–13% over the initial 3-year time span, and 23% over 6 years. Annualized decline on the domains ranged from -6% (Knowledge of Assets/Estate) to -22% (Investment Decision-Making) at 3-year follow-up, and from -14% (Basic Monetary Skills) to -37% (Financial Judgment) over 6 years. Conclusion(s): Over a six-year period MCI patients demonstrated significant declines in multiple financial skills-in particular financial judgment. The findings highlight the importance of early MCI diagnosis and corresponding immediate attention by clinicians and family members to oversight of a patient's financial activities and protection of assets.