In this paper we present the sex and age-at-death structure of the Aquihuecó archaeological burial site and discuss its implications for the population dynamics of northwestern Argentinian Patagonia at the beginning of the Late Holocene. The site is located on a sand-dune in the Curi Leuvú River valley (Neuquén Province) and has been defined as a burial site with a chronology that spans from 4304 ± 59 to 3650 ± 70 years BP. A minimum number of 64 individuals was estimated, including fragmentary bone remains spread on surface, and a mortality curve was built based on 43 skeletons in situ. Both sexes and all age categories, except the range 15-19.9 years, are represented in the sample. The mortality curve is characterized by a bimodal pattern with two peaks corresponding to the ranges 0-4.9 years (20.92%) and 25-29.9 (11.63%). The Juvenile/Adult Ratio and the Mean Childhood Mortality were calculated in order to characterize the population dynamics. Although both indices indicate a biased sample, other evidences (i.e. molecular, radiocarbon, isotopic and zooarchaeological) suggest it is growing population. The mortality curve was compared with those obtained for sites located in neighboring areas. The pattern is similar, but no statistically significant correlations were found.