Background: The intergenerational transmission of fertility has received much attention in demography. This has been done by estimating the correlation between parents’ and offsprings’ fertility. An alternative method that provides a more comprehensive account of the role of family background - sibling correlations - has not been used before.

Objective: I estimate the overall importance of family background on entry into parenthood and completed fertility and whether it changed over time. Furthermore, I compare the intergenerational correlation in completed fertility with corresponding sibling correlations.

Methods: Brother and sister correlations in first birth hazard and in final family size were estimated using multi-level event-history and multi-level linear regression on Swedish longitudinal register data.

Results: The overall variation in fertility that can be explained by family of origin is approximately 15%-25% for women and 10%-15% for men. The overall importance of the family of origin has not changed over the approximately twenty birth cohorts that were studied (1940-63 for women, 1940-58 for men). Parents’ completed fertility accounts for only a small share of the total family background effect on completed fertility.

Conclusions: This study contributes to the existing understanding of intergenerational transition of fertility, both methodologically, by introducing a new and powerful method to study the overall importance of family of origin, and substantially, by estimating the overall importance of family of origin and ist development over time. A non-negligible proportion of the variation in fertility can be attributed to family of origin and this effect has remained stable over twenty birth cohorts.