Since the onset of democracy in 1975, both total fertility and Mass attendance rates in Spain have dropped dramatically. I use the 1985 and 1999 Spanish Fertility Surveys to study whether the significance of religion in fertility behavior – both in family size and in the spacing of births – has changed. While in the 1985 SFS family size was similar among practicing and non-practicing Catholics, practicing Catholics portray significantly higher fertility during recent years. In the context of lower church participation, religiosity has acquired a more relevant meaning for demographic behavior. Among the youngest generation, non-practicing Catholics behave as those without affiliation. The small group of Protestants and Muslims has the highest fertility and interfaith unions are less fertile.