The female athletic triad refers to the interaction between menstrual function, energy availability and bone density. When an imbalance appears between energy input and output, the global health of the athletic teenager is at risk of somatic and/or psychological complications as defined by the RED-S (Relative Energy Deficiency in Sports). In athletic girls menstrual disorder should be seen as an alert. It may be difficult to distinguish it from menstrual irregularity due to immature hypothalamic-hyphophysic-gonadal axis, which can be physiological at that age. A multidisciplinary approach is needed. The challenge is to find a balance between sport practice and prevention of complications due to lack of estrogens.