This article provides the basic elements for the discussion and analysis of medical systems and their inter-dependency, with special reference to Latin America and, in particular, to the Andean countries. In a culturally diverse and socially stratified population, such as in contemporary Latin America, medical systems constitute a social representation resulting from the historical relationship between autochtonous medical cultures and those from other latitudes. The impregnation of scientific and popular knowledge results not only in the incorporation (and often expropriation) of folk in professional or scientific medicine, but also in the increasing 'medicalisation' of popular and traditional therapeutic practices. The emergent 'popular' medical system draws from both the professional and folk models, and in its actual practice, integrates both popular beliefs and materia medica with elements drawn from popular religions and pre-Hispanic deities. The degree of competitiveness, co-operation or 'integration' among medical systems depends mainly on the asymmetrical distribution of power and resources, and is conditioned by the population's behaviour in the management of disease. Existing pluralist systems of health care reveal a valuable array of survival strategies, which far outreach the proposals for integration called for by official sectors. On the other hand, knowledge derived from traditional medicine can contribute to the development of new models of clinical practice and to the expansion of the conventional epidemiological model.