Using a unique 12-years panel of personnel records from a large French company, we find that becoming mother (extensive fertility margins) largely affects labor market outcomes. Instead, fatherhood does not significantly impact on men's wages or careers. An event study approach with the use of non-parents as control group enables us to show that, prior to childbirth, future mothers' earnings are in line with that of non-mothers. However, one year after birth, they start to fall, reaching -9% in total pay and -30% in individual bonuses. This drop is persistent: 8 years after childbirth there is no evidence of a catching-up trend. Mothers also have lower chances to climb-up the hierarchy of the firm and be promoted to managerial positions. A decomposition of the motherhood penalty shows that these \missed promotions", likely due to an increase in absenteeism during the child's pre-school age, are the main determinants of mothers' lower outcomes within the firm.