Similar results arise with the Nopo decomposition, most of the motherhood wage penalty in the informal sector is unexplained, and when we add more characteristics to the match it is greater than the actual gap (A = -14.4% and A0 =-17.5%). Their vulnerability is observed not only in their wages, which are lower than formal-sector women’s, but also in a motherhood wage penalty that rises with the number of children and is greatest when children are young. Institutional labour market rules thus appear to be a crucial determinant of wages for women in Buenos Aires.