In several developed countries, the ageing process of the population may pose fiscal risks to the PAYG systems of public pensions. This paper studies the determinants of two forms of accessing retirement in Spain, either partial or full retirement. Our goal is to identify if social security legislation influences the choice between these two alternative paths. Using a newly released data set we estimate a multinomial logit duration model including different measures capturing the economic incentives embedded in the social security system. Our results show that social security incentives determine individual retirement decisions. Besides, partial retirement legislation modifies the selection of retirement routes and affects the age of retirement moving it to an earlier date.