Background: In individuals with only mild or very mild cognitive attenuations (i.e., so-called pre-clinical AD), performance-based measures of function may be superior to informant-based measures because of increased sensitivity, greater reliability, and fewer ceiling effects., Objective: We sought to determine if a performance-based measure of everyday function would demonstrate adequate psychometric properties and validity in the context of serial assessment over a one-year period in patients with Mild Cognitive Impairment (MCI) and early stage Alzheimer's disease (AD)., Design: Participants were assessed with the performance-based measure at baseline, six weeks, and one year., Setting: A specialized center for the assessment and treatment of AD., Participants: Three groups of subjects participated: a healthy subjects (HS) older cognitively intact group (N=43), an MCI group (N=20), and an AD group (N=26)., Measurements: A three subtest short form of the UCSD Performance-Based Skills Assessment (UPSA) (called the UPSA-3) was the measure of interest. It consisted of the Communication, Planning, and Finance subtests., Results: Mixed model repeated measures were used to assess performance over time. Large group effects were present (HS>MCI>AD). Additionally, the AD and MCI groups demonstrated declines over one year, while the HS group remained stable (group x time interaction p=.11). The MCI/AD group demonstrated adequate test-retest reliability and did not demonstrate ceiling or floor effects., Conclusion: Our data indicate that the UPSA-3 is suitable for clinical trials in that it has adequate ecological coverage and reasonable psychometric properties, and perhaps most importantly, demonstrates validity in serial assessments., Competing Interests: Dr. Goldberg has received funding from Neurocog Trials for consulting on functional competence measures for Alzheimer’s disease and royalties for the use of the Brief Assessment of Cognition in Schizophrenia (BACS) in clinical trials. Dr. Devanand is a consultant for Acadia, Eisai, Avanir, Genentech, Neuronix, and Grifols. He receives Research Support from National Institute of Aging. Dr. Harvey has received consulting fees or travel reimbursements from Alkermes, Boehringer Ingelheim, Intra-Cellular Therapies, Jazz Pharma, Minerva Pharma, Otsuka America, Sanofi Pharma, Sunovion Pharma, Takeda Pharma, and Teva during the past year. He receives royalties from the Brief Assessment of Cognition in Schizophrenia. He is chief scientific officer of i-Function, Inc. He has a research grant from Takeda and from the Stanley Medical Research Foundation. Dr. Richard Keefe currently or in the past 3+ years has received honoraria, served as a consultant, speaker, or advisory board member for Abbott Labs, Abbvie, Abide Therapeutics, Acadia, Aeglea Bio Therapeutics, Akebia, Akili Interactive Labs, Alkermes, Allergan, Amgen, Aptinyx, Armagen, Astellas, Asubio, Avanir, AviNeuro/ChemRar, Axovant Sciences, Biogen Idec, BiolineRx, Biomarin, Biomimetix, Boehringer-Ingelheim, Braincells, Bristol-Myers Squibb, Cerecor, CHDI, Composite Type, Critical Path Institute, Eli Lilly Laboratories, FORUM, Gammon, Howard and Zeszotarski, Global Medical Education, GW Pharmaceuticals, Helicon, Idorsia, Intra-Cellular Therapies, Janssen, JCR, Karuna, Kempharm (DCRI), LSK Global, Lundbeck, Lysogen, MedScape, Memory Pharmaceuticals, Mentis Cura, Merck, Merrakris Therapeutics, Minerva, Mitsubishi, Montana State University, Moscow Research Institute of Psychiatry, Neuralstem, Neuronix, NeuroSearch, New York State Office of Mental Health, Novartis, Orion, Orygen, Otsuka, Paradigm Testing, Parexel, Percept Solutions, Pfizer, Pharm-Olam, PsychoGenics, Regenxbio, Renuron, Reviva, Roche, Sangamo, Sanofi, Science 37, Shire, Six Degrees Medical, SOBI, Solvay, Sunovion, Takeda, Targacept, Teague, Rotenstreich, Stanaland, Fox and Holt, Thrombosis Research Institute, University of Moscow, University of Southern California, University of Texas Southwest Medical Center, WebMD, Wilson Therapeutics, and Wyeth. Dr. Keefe has currently or in the past 3+ years received research funding from Allon, Astra Zeneca, Boehringer-Ingelheim, Department of Veteran’s Affairs, Feinstein Institute for Medical Research, GlaxoSmithKline, National Institute of Mental Health, Novartis, Psychogenics, Research Foundation for Mental Hygiene, Inc., and Singapore Medical Research Council. Dr. Keefe receives royalties from versions of the BAC testing battery, the MATRICS Battery (BACS Symbol Coding), and the Virtual Reality Functional Capacity Assessment Tool (VRFCAT). Dr. Keefe is a shareholder in VeraSci and Sengenix