OBJECTIVES: To empirically assess the capacity of patients with amnestic mild cognitive impairment (MCI) to consent to medical treatment under different consent standards (Ss). METHODS: Participants were 56 healthy controls, 60 patients with MCI, and 31 patients with mild Alzheimer disease (AD). Each participant was administered the Capacity to Consent to Treatment Instrument (CCTI) and a comprehensive neuropsychological battery. Group differences in performance on the CCTI and neuropsychological variables were examined. In addition, the capacity status (capable, marginally capable, or incapable) of each MCI participant on each CCTI standard was examined using cut scores derived from control performance. RESULTS: Patients with MCI performed comparably to controls on minimal consent standards requiring merely expressing a treatment choice (S1) or making the reasonable treatment choice [S2], but significantly below controls on the three clinically relevant standards of appreciation (S3), reasoning (S4), and understanding (S5). In turn, the MCI group performed significantly better than the mild AD group on [S2], S4, and S5. Regarding capacity status, patients with MCI showed a progressive pattern of capacity compromise (marginally capable and incapable outcomes) related to stringency of consent standard. CONCLUSIONS: Patients with amnestic mild cognitive impairment (MCI) demonstrate significant impairments on clinically relevant abilities associated with capacity to consent to treatment. In obtaining informed consent, clinicians and researchers working with patients with MCI must consider the likelihood that many of these patients may have impairments in consent capacity related to their amnestic disorder and related cognitive impairments. ©2007AAN Enterprises, Inc.