Background: During rugby, female breasts will be exposed to injury through direct blows. Whilst breast injury is prevalent in contact sports, they predominantly go unreported. Research has focused on senior players and therefore prevalence in adolescents is not well known. Aims: This study investigated the prevalence, mechanism, and reporting behaviours of breast injury in under-18 women’s rugby union. Methods: A custom designed questionnaire was completed by 83 international female players, who were competing at the Under-18 Women’s Six Nations Festival in North Wales. Players were aged between 16 and 18 years old. Retrospective data on breast injuries and prevention strategies were collected. Results: Forty-four percent of players (n = 36) reported previously sustaining a breast injury whilst playing rugby, with 75% (n = 27) reporting > 1 injury in the past year. Sixty-one percent (n = 22) of players reported their most severe injury healed within 1-2 weeks. Contact with another athlete was the most reported contributing factor (84%, n = 32), followed by direct contact with the ground (51%, n = 1). Seventy-six percent (n = 25) of players did not report their most severe breast injury, with those who did informing either a parent (n = 7) or a teammate (n = 2). No injuries were reported to a coach or medical professional. Sixty percent (n = 49) of players considered themselves not to use any strategies to prevent breast injury with only 10% (n = 8) reporting wearing female specific protective armour. Conclusion: Breast injury is common in adolescent women’s rugby, which highlights the need for more research into its effects on the developing breast. Adolescent players rarely report injuries to medical professionals. Increased awareness of breast injury and its potential impact may encourage reporting. Breast injury management and prevention strategies should be developed to reduce the occurrence in these athletes.