The Open Access Series of Imaging Studies (OASIS) is a series of MRI data sets that is publicly available for study and analysis. The present data set consists of a longitudinal collection of 151 subjects aged 60 to 98. Each subject was scanned on two or more visits, separated by at least one year. All subjects were characterized using the Clinical Dementia Rating (CDR) are either nondemented or with very mild to mild dementia of the Alzheimer’s type (DAT). 77 of the subjects were characterized as nondemented at the time of each of their visits. 64 of the included subjects were characterized as demented at the time of their initial visits and remained so for subsequent scans. Another 10 subjects were characterized as nondemented at the time of their initial visit and were subsequently characterized as demented at the time of one or more later visits. The subjects were all right-handed and include both men (n=62) and women (n=89). For each scanning session, 3 or 4 individual T1-weighted MRI scans were obtained. Multiple within-session acquisitions provide extremely high contrast-to-noise making the data amenable to a wide range of analytic approaches including automated computational analysis. Automated calculation of whole brain volume and estimated total intracranial volume are presented to demonstrate use of the data for measuring differences associated with normal aging and Alzheimer’s disease.