Alcmaeon, a philosopher-cum-doctor from Croton, offers the earliest known definition of health and disease. The aim of this paper is to examine the formulation of his medical theory in terms of political organization, namely the polarity between one-man rule and egalitarianism , by taking into account contemporary philosophical and medical texts, as well as the historical context. The paper is divided into four sections. I first overview the compendium in which this medical theory is reported, trace the doxographical layers, and (...) analyse the terminology employed . I then focus on the key aspects of this medical theory, including the constitution of the body, the interaction of opposites, and the aetiology of disease . I suggest that Alcmaeon's notion of equality can be understood in various ways, and discuss the possible interpretations in the light of early Greek philosophy and medicine. The most likely interpretations are that there exists a kind of equilibrium between pairs .. (shrink)