Cognitive dysfunctions in old individuals can be a precursor of dementia. The Maastricht Aging Study (MAAS) was designed to characterize the usual and pathological aging of cognitive function. The study involves a group of 1,900 initially healthy individuals who will be followed-up for a period of 12 years with respect to health characteristics and neurocognitive status. For this purpose a sample was drawn from a patient register of collaborating family practices, stratified for age (range 24 to 81 years), sex and general ability level. Rationale and design of MAAS are discussed and also some findings from the cross-sectional baseline measurement: general aspects of memory and attention, cognitive functioning after brain trauma and general anesthesia, physical condition (fitness, morbidity and vascular risk factors) as predictor of cognitive function, and finally cognitive complaints and metamemory.