Long cycles and excessive uterine bleeding are the most common menstrual disorders in adolescents. Long cycles usually result from a benign transitory functional disorder which spontaneously resolves within two to three years after menarche; however, this diagnosis can only be retained in the absence of hirsutism or galactorrhea as revealing symptoms of functional ovarian hyperandrogenism, polycystic ovary syndrome, late form of congenital adrenal hyperplasia or hyperprolactinemia; ovarian failure will be considered in case of isolated long cycles persisting more than two years after menarche. Excessive uterine bleeding usually occurs early after menarche. Although the main cause is functional, resulting from anovulation and the related absence of progesterone, coagulation disorders must always be excluded. Management of these disorders are described.