Taking a historical perspective this paper examines the ecological and political influences on Mongolian demography. Changes in political policy, domestic economy, health services, venereal diseases and shortages of men are considered in examining the unusual pattern of very low fertility, followed by a rise in the 1950s and 1960s and a gradual fertility decline, even in the absence of modern contraception. It is concluded that the lack of simultaneity between major political and demographic changes suggest that there are no direct responses to policy, despite the strong pronatalist stance, but that health services, particularly in the realms of venereal disease treatment, have had a major influence on Mongolian demographic patterns. The indirect consequences of government policy—education, health services in rural areas, rapid urbanisation—appear to have a stronger influence than the pronatalism, and ironically have led to rapid fertility decline.