The relationship between modernization and childlessness is examined for the 32 states of Mexico for 1970. Earlier reports are cited and present childlessness as a predominantly involuntary phenomenon in developing countries. It is hypothesized that a negative correlation exists between socioeconomic development and an ability to reproduce hence reduced childlessness. The 1970 Mexican census established the number of births. Subjects were ever married women--women who were married widowed divorced separated or living in consensual unions. 4 factors represent modernization: structural economic development; health conditions; health facilities/economic activity/railroads; and transportation. Analyzing childlessness against these criteria shows a decline in childlessness correlated with increased work force participation urbanization more widespread transportation increased educational levels and most significant an increase in health care facilties. Health conditions were the most accurate barometer of childlessness. Better health care meant reduced incidence of disease and nutritional deficiencies the 2 major causes of subfecundity. Changes in fertility which accompany modernization should be considered in the design and evaluation of a family planning program.