Menarche, the onset of menstruation is a fundamental part of a girl's transition from childhood to adolescence. Studies show that girls in many countries experience menarche with insufficient information and support. Girls from around the world report feeling ashamed and afraid. The potential health effects of such experiences include a weakening of girls' sense of self-confidence and competence, which in turn may comprise girls' abilities to assert themselves in different situations, including in relation to their sexuality and sexual and reproductive health. There is an important need for the public health community to assure that girls receive the education and support they need about menstruation, so they are able to feel more confident about their bodies, and navigate preventable health problems - now and in the future. For too long, the global health community has overlooked the window of opportunity presented by menarche. Family planning programs have generally focused their efforts on married couples and HIV programs have focused safer sex promotion on older adolescent girls and boys. Starting the conversation at menarche with girls in early adolescence would fully use this window of opportunity. It would engage young adolescent girls and be a natural first step for later, more comprehensive conversations about sexuality, reproduction and reproductive health. There are a number of initiatives beginning to tackle the provision of puberty information to girls and boys, but the global health community is overdue to set a global standard for the provision of such guidance.