The objective of this paper is to quantify the opportunity cost of girls' exclusion from productive employment with the hope that stark figures will lead policymakers to reconsider the current underinvestment in girls. The paper explores the linkages between investing in girls and potential increases in national income by examining three widely prevalent aspects of adolescent girls' lives: early school dropout, teenage pregnancy and joblessness. The countries included in the analysis are: Bangladesh, Brazil, Burundi, China, Ethiopia, India, Kenya, Malawi, Nigeria, Paraguay, Senegal, South Africa, Tanzania, and Uganda.