Tierra del Fuego is situated at the southern tip of the American continent, which conditions its environmental and climatic characteristics. The colonizing population arrived, at the end of the 19th century, from other Chilean regions (particularly from Chiloe) and diverse European countries, especially Britain and Croatia, but also Germany, Spain and Italy. In the present study, the existence of a seasonal pattern in 5430 births registered in the Chilean population of Tierra del Fuego from 1890 to 1995 was analysed. The analysis showed no seasonal distribution of births in the periods 1890-1920 and from 1946 to the present day, a phenomenon rarely reported in the literature. The absence of seasonality in birth distribution could be related to the great diversity in the origins of the population's families, the constant renovation of this and the declining importance of the administrative capital of the province of Tierra del Fuego, Porvenir, in favour of Punta Arenas, capital of the Magellanic region. In the period of maximum development of the capital of the province, a seasonal pattern was detected with a peak in April and a trough in October, which corresponds with a maximum of conceptions in July and, in general, during the early southern winter and a decline in births from late spring to mid-summer, with a trough in January. This birth distribution is interpreted as a subordination of activity and social life to the annual sheep cycle. In addition to temporal trends, the influence on the observed patterns of environmental parameters, father's occupation, seasonality of marriage and the origin of the parents were analysed.