Abnormal uterine bleeding is a common problem in adolescents. The differential diagnosis varies from pregnancy and infection to anovulation and coagulopathy. Careful history and examination can help elucidate the best next steps for workup and management. Heavy menstrual bleeding is particularly worrisome in this group not only when it occurs at menarche, but also anytime afterward when bleeding lasts longer than 7 days, blood loss is greater than 80 mL per cycle, or other warning signs that indicate a history of heavy bleeding such as anemia. Once conditions of pregnancy, infection, structural abnormalities, and hormonal causes have been ruled out, first-line treatment is medical management with hormonal therapy or nonhormonal options. Invasive measures are a last resort in this patient population, because maintenance of fertility is of critical importance.