This paper analyzes the effect of the number and age structure of children on women's income in Colombia.On average, mothers earn 17.6% less than non-mothers.Since not all women participate in the labor market, sample selection is a potential issue that is, therefore, corrected.The empirical results confirm the existence of a significant wage penalty for motherhood.After controlling for observables and sample selection, an income gap of 9.4% between mothers and non-mothers remains.This gap is wider when the children are under 5 years old, 18.4%.This gap is partly explained by the fact that mothers are more likely than non-mothers to be employed in lower quality jobs in which they do not contribute to health care and pension, as well as by the fact that being a mother substantially increases household responsibilities for women.