South American Archaeology Series No 23 Reliable sex and age estimate on human bone remains is a fundamental aspect in bioarchaeological investigation since such estimates represent the basis on which supplementary studies aiming at contributing to the knowledge of biological and cultural aspects of prehistoric populations are structured. However, since many features, both metrical and morphological ones are specific for each population, and knowing that growth and development patterns as well as sexual dimorphism vary among groups, this work aims at understanding sex and age biological markers on archaeological osteological collections from the Northwest of Argentina. These collections are made up of different sets of skeletons belonging to native populations and fitting different time periods. The fundamental objective of this work has been to study the behavior of sex and age variability general pattern inside and among the collections observed, and, therefore, basic information concerning age and sex patterns of the whole population set they belong to can be provided.