This paper uses data from PISA and the OECD Survey of Adult Skills (PIAAC) to examine the evolution of socio-economic and gender disparities in literacy and numeracy proficiency between the ages of 15 and 27 in the sample of countries that took part in both studies. Socio-economic disparities are exacerbated between the age of 15 and 27 and the socio-economic gap in proficiency widens, particularly among low-achievers. Gender disparities in literacy at age 15 are marked across the performance spectrum but are particularly wide among low-performers. However, by age 24 there is no difference in the literacy proficiency of males and females. The gender gap in numeracy at age 15 is quantitatively small when compared with the gap in literacy, although it is more pronounced among high achievers. The paper canvasses possible explanations for the trends observed and discusses implications for policy and practice, including the extent to which the lack of an established link between PISA and PIAAC limits the analytical value of the two studies.