Health research on an increasingly aging population calls for careful consideration of aging-associated phenomena, such as dementia. Accounting for such diseases is a necessary step for gaining a view of health in the elderly. It is moreover imperative to gather data on subjects' mental limitations in surveys to better evaluate the validity of answers disclosed by elderly participants. This article discusses the availability of data on individuals suffering from dementia in national studies on aging. It centers on the question of how surveys respond to the challenge of diagnosing dementia. The analysis is based on a literature review, which focuses on national studies on aging that were conducted no later than 2005, and that enforced an upper age limit of at least 79 years old for their subjects. By evaluating these published studies, and analyzing their data descriptively, it was determined how many subjects suffering from dementia were part of each sample, and which methods were applied to diagnose such illnesses. Overall, the availability of data on age and aging is satisfactory in Germany. The literature review discovered seven studies on aging, as well as five that lend themselves to a framework oriented toward research on aging. The number of subjects suffering from dementia in the samples is between 0 and 14% - over half of the studies reach less than 1.5% of those affected. These results thus point out problems in surveying individuals suffering from dementia. They highlight the limitations of studies on aging that do not account for dementia in their subjects. The following discussion aims to contribute to the debate on relevant research methodology, and to the development of methodological approaches that consider dementia as a crucial factor.