The normal ovulatory menstrual cycle requires the presence of a mature hypothalamic-pituitary-ovarian axis and highly coordinated hormonal feedback loops. Consisting of three phases (follicular, ovulatory, and luteal), the normal menstrual cycle results in the formation of a mature follicle and release of an oocyte during each cycle, with menses occurring in the absence of fertilization. While adolescents may initially experience anovulatory cycles following menarche, the vast majority of cycles will be fairly regular, lasting 21 to 45 days in length with an average of three to seven days of bleeding. Absence of menarche by age 15, absence of menses for three consecutive months, and menses lasting eight days or longer with or without associated heavy bleeding are among the menstrual abnormalities that warrant further evaluation. Obtaining the menstrual history in adolescents with the knowledge of expected menstrual patterns allows the pediatric practitioner to provide appropriate counseling and education to adolescents and their families, and to identify menstrual abnormalities when they arise. Treating the menstrual cycle as a “vital sign” highlights the importance of normal menses as an indicator of an individual's overall health and enables timely identification of any concerning findings.