We study the earnings and career profiles of employees who experience the birth of thefirst child, as compared to their childless co-workers. Using a difference-in-differencesapproach and a unique12-year panel of personnel records from a large French company, we find that the arrival of a child creates a persistent penalty in earnings for mothers. The gap in internal promotions, both at the extensive and intensive margin, accounts for thevast majority of the motherhood penalty within the firm. We believe that firm-level policieson child-related leaves, if not gender neutral, can exacerbate the motherhood penalty.