Socio-economic differentials in fertility are examined by using data collected from a daily registration system covering over 100,000 persons in rural Bangladesh during the period 1968 to 1970. The findings indicate that fertility was generally higher among women in the higher than in the lower socio-economic groups. Several factors associated with high socio-economic status and their relation with the intermediate variables are discussed as providing the linkages with high fertility. These include, health status, breastfeeding, the enforcement of ‘purdah’ and migration.