This article investigates, for the case of Spain, to what extent the introduction in March 2007 of a non-transferable 13-day paternity leave has encouraged men to make greater use of childbirth leave. Data were drawn from the Spanish Economically Active Population Survey, covering the period 2005–2009. We use a natural experiment approach, comparing the behavior of wage earners fathers with children of less than 1 year of age before and after the reform and using mothers as control group. After estimating a difference-in-differences logistic regression model we obtain statistical evidence that there is a higher percentage of males on leave in the reference week in the post-reform period (after 2007). The article also analyzes some of the personal and socio-economic determinants of the fathers’ use of childbirth leave. Fathers are more likely to be on leave if they have stability in employment, if there are facilities for reconciling work and family life (working in the public sector) and if the partner is employed. The father’s age has an interesting U-shaped influence.