AbstractObjectiveTo examine the reliability and validity of the mCDR, a modified version of the clinical dementia rating (CDR) scale.MethodsThe mCDR is an informant‐based, technician‐administered, structured interview with multiple choice responses, which does not include objective cognitive testing. Subjects (n = 556) with no cognitive impairment (NCI), amnestic mild cognitive impairment (aMCI), and dementia were assessed with mCDR, CDR, and neuropsychological evaluation, while medial temporal atrophy (MTA) was measured on MRI scans. The mCDR and CDR were compared with respect to inter‐rater reliability, validity, and ability to predict progression in cognitive diagnosis at 12 month follow‐up.ResultsThe mCDR can be administered in less than one third of the time required to administer the CDR (30 min). Inter‐rater reliability (Cohen's weighted κ) was 0.86 for the mCDR and 0.56 for the CDR. Ability to distinguish between NCI, aMCI, and Dementia subjects, and correlations to memory and non‐memory measures were marginally better for the CDR, in comparison to the mCDR. Correlations of mCDR and CDR scores to MTA scores did not differ. Baseline mCDR scores predicted transition from NCI to aMCI, whereas baseline CDR scores predicted transition from aMCI to Dementia.ConclusionsThe mCDR, as compared to the CDR, is briefer and more reliable, and is a valid measure of functional ability among subjects with normal cognition, mild cognitive impairment, and mild dementia. The mCDR should be particularly useful as a reliable and economical instrument for assessing change in functional abilities, especially in multi‐center clinical trials and population studies of MCI and mild dementia. Copyright © 2009 John Wiley & Sons, Ltd.