This article explores the connection between labour market segregation and motherhood wage penalties in Argentina across the formal and informal sectors. It uses ordinary least square and quantile regression estimation strategies and deploys Blinder-Oaxaca and Ñopo decompositions to identify sources of wage differences. The finding is that there is strong evidence of labour market segmentation and that motherhood wage penalties differ substantively across the sectors and between different wage quantiles. In particular, formal-sector working mothers do not experience wage penalties, while informal ones do. The motherhood wage penalty increases with the number of children, especially younger children, and is greatest at the bottom and next greatest at the top of the conditional wage distribution.