[Longitudinal studies on aging: past, present and future].

Longitudinal studies on aging have played an important role in the development of gerontology and geriatrics, and have multiplied in the last 30 years. This is related to methodological advantages of this type of design and to issues closely connected to geriatrics itself. The understanding of the complex process of aging and its associated clinical and functional consequences, which are usually slow, requires a sufficiently long observation and follow-up. In this article, along with historical and methodological aspects, we examine possible future lines development for longitudinal studies on ageing.