The Maastricht Aging Study (MAAS) was designed to specify the usual and pathological aging of cognitive function. In short, the main questions of MAAS are: who deteriorates when in which aspects of cognitive function, and what biomedical or psychosocial factors can be identified that may act as mediators in this process? The study comprises four independent panel studies in which a group of 1,900 initially healthy individuals are followed 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 general practitioners, stratified by age (range 24 to 81 years), sex and general ability level. Rationale and design of MAAS are discussed and some findings from the cross-sectional baseline measurement are summarized: general aspects of memory and attention in aging, cognitive functioning after brain trauma and general anesthesia, physical condition (fitness, morbidity and vascular risk factors, such as blood pressure) as predictors of cognitive function, and finally cognitive complaints and metamemory.