The joint industry/NIH funded Alzheimer’s Disease Neuroimaging Initiative (ADNI) is a longitudinal cohort study created expressly to investigate cerebrospinal fluid and volumetric neuroimaging measurements as diagnostic biomarkers of early Alzheimer’s disease (AD) and as potential endpoints for monitoring clinical trial treatment effects. Using ADNI data we show that various neuroimaging measures track disease progression well, and are substantially more precise than traditional cognitive and functional measures. Based on power calculations for treatment effects defined in terms of percentage slowing of progression of the measures, clinical trial using neuroimaging measures such as hippocampal volume would require a fraction of the number of subject as required using cognitive scales, suggesting the potential utility of imaging measures from the statistical efficiency perspective.