In recent years, an increasing number of medical books and papers attempting to analyse the concepts of health and disease from the perspective of evolutionary biology have been published (Eaton et al., 1993; Ewald, 1993; Harrison, 1993; Nesse and Williams, 1995; Profet, 1991; Rose, 1991; Temple and Burkitt, 1994). This paper introduces the evolutionary approach to health and disease in an attempt to illuminate the premisses and the framework of Darwinian medicine. My primary aim is to analyse to what extent evolutionary theory provides for a biological definition of the concept of disease. This analysis reveals some important differences between functional explanations in the field of evolutionary biology and functional explanations in the field of medicine. Moreover, I shall argue that the biological functions relevant to the health of an organism cannot be determined on the basis of evolutionary theory. Accordingly, it seems that Darwinian medicine does not provide for the definition of a biological concept of disease. Still, Darwinian medicine may suggest why we are susceptible to certain diseases; it might also prove a suggestive heuristic on the basis of which new hypotheses concerning relevant treatments of various diseases might be advanced.