The Toba represent one of the many indigenous groups inhabiting the Gran Chaco of South America. They currently live in communities with different degrees of acculturation. We present here a preliminary data on fecundity and mortality estimates for a rural Toba population located in the province of Formosa, Argentina. Reproductive histories (n = 435) were obtained from villagers 12 years old and older. Reproductive histories were cross-checked with other sources such as national identification documents, health records kept at the local health center, and previous censuses to verify the information obtained. The analysis presented here includes data from 1981 to 2002. We estimated the crude birth rate, total fertility rate, the crude death rate, and the rate of population growth. The results show high rates of population growth determined by pre-transitional values of birth and fertility rates and a decrease in mortality rates. This reduction in mortality may be attributed to a slow improvement of life conditions among the Toba, in particular, access to health care and food security. The first two periods analyzed indicated a mild immigration pattern, while in the rest of the years there was a strong emigration. This finding would reflect a situation of crisis and social tensions within and outside the Toba population. This study can contribute to our understanding of demographic dynamics in populations which are experiencing a rapid lifestyle transition; in this case, from a hunter-gatherer recent past to a market economy future.