The nature of the relationship between land tenure and fertility in an important contemporary setting is examined. Examination of the institutional structure of the Mexican land tenure system reveals some features that could have a positive impact on fertility. The possible pronatalist bias of the system is identified and discussed and the hypothesis that the population in the land reform sector exhibits higher fertility than other comparable populations in Mexico is tested. Tests are performed over 2 data sets using various measures of fertility; results more or less uniformly reject the null hypothesis that the fertility of the land reform sector families does not differ from other families. The empirical evidence strongly suggests that the percentage of ejidatarios (people belonging to an agrarian community that has received and continues to hold land in accordance with the agrarian laws growing out of the Revolution of 1910; this structure embodies several possible pronatalist incentives because of attenuated property rights) in a given population affects both the number of children ever born to women and the stock of children per woman of prime bearing age. While this statistical evidence can be explained by many alternate hypotheses it does support an economic interpretation of the decision to bear children. The constant competition for better land within the ejido together with a desire to secure a legal renter or inheritor for the land may be factors that induce ejidatarios to have larger families than private farmers or paid agricultural workers. It is significant that the very rapid population growth in Mexico has coincided with extensive reallocations of land to the ejidos from the private sector.