We present the first results of one ethnographic research centered in representations and practices about health/illness processes in the firsts stages of the life cycle, in two Mbyá – Guaraní communities from the Province of Misiones, Northeastern Argentina. Indicators which might identify the different stages of the life cycle were searched from a local perspective and the following factors were found as relevant: behaviour, activities and places adequate or inadequate according to sex and age, alimentary prescriptions and prohibitions, related to certain health/illness processes. In connection to this, we obtained information about some child care practices intended to prevent illnesses and protect children of several ages in different risky situations. An initial analysis and evaluation of this information made us propose hypothesis about the relation between these factors and the health-illness processes in the first stages of life.