OBJECTIVES: Research estimates that a significant percentage of individuals with mild cognitive impairment (MCI) experience functional difficulties. In addition to reduced accuracy on measures of everyday function, cross-sectional research has demonstrated that speed of performing instrumental activities of daily living (IADLs) is slowed in individuals with MCI. The present study investigated whether baseline and longitudinal changes in speed and accuracy of IADL performance differed between persons with MCI and cognitively normal peers. DESIGN: Linear mixed models were used to estimate the group differences in longitudinal performance on measures of IADLs. SETTING: Assessments were conducted at university and medical research centers. PARTICIPANTS: The sample consisted of 80 participants with MCI and 80 control participants who were enrolled in the Alzheimer's Disease Research Center's Measuring Independent Living in the Elderly Study. MEASUREMENTS: Instrumental activities of daily living speed and accuracy were directly assessed using selected domains of the Financial Capacity Instrument, the Timed IADL assessment, and driving-related assessments (Useful Field of View, Road Sign Test). RESULTS: Individuals with MCI performed worse on speed and accuracy measures of IADLs in comparison to cognitively normal peers and demonstrated significantly steeper rates of decline over three years in either speed or accuracy in all domains assessed. CONCLUSION: Both speed and accuracy of performance on measures of IADL are valuable indices for early detection of functional change in MCI. The performance pattern may reflect a trade-off between speed and accuracy that can guide clinical recommendations for maintaining patient independence.