We examine the relationship between cognitive ability and childbearing patterns in contemporary Sweden using administrative register data. The topic has a long history in the social sciences and has been the topic of a large number of studies, many reporting a negative gradient between intelligence and fertility. We link fertility histories to military conscription tests with intelligence scores for all Swedish men born 1951 to 1967. We find a positive relationship between intelligence scores and fertility, and this pattern is consistent across the cohorts we study. The relationship is most pronounced for the transition to a first child, and men with the lowest categories of IQ-scores have the fewest children. Using fixed effects models we additionally control for all factors that are shared by siblings, and after such adjustments we find a stronger positive relationship between IQ and fertility. Furthermore, we find a positive gradient within groups at different levels of education. Compositional differences of this kind are therefore not responsible for the positive gradient we observe - instead the relationship is even stronger after controlling for both educational careers and parental background factors. In our models where we compare brothers to one another we find that, relative to men with IQ 100, the group with the lowest category of cognitive ability have 0.58 fewer children, and men with the highest category have 0.14 more children.