HIDDEN FRAILTY: MYTHS AND REALITY by Anatoli I. Yashin 1,2 , Ivan A. Iachine 3 , Alexander Z. Begun 1 , and James W. Vaupel 1,4 1 Max Planck Institute for Demographic Research, Rostock Germany; 2 Duke University, Center for Demographic Studies, USA; 3 University of Southern Denmark, Department of Statistics and Demography, Odense, Denmark; 4 Duke University, Sanford Institute, USA Correspondence should be directed to: Prof. A. Yashin, Max Planck Institute for Demographic Research Doberaner Str. 114, 18057 Rostock, Germany e-mail: yashin@demogr.mpg.de; fax: +49 381 2081 169; phone: +49 381 2081 106 Acknowledgments This research was partly supported by NIH/NIA grant PO1 AG08791-01. The authors thank Baerbel Splettstoesser and Karl Brehmer for help in preparing this paper for publication. Synopsis. In this paper we discuss the notion of individual frailty and its interpretation. In addition, we consider the application of this concept to different areas of demography, epidemiology, and the genetics of aging. 1