DefinitionAmenorrhea is the absence of menstruation. Menstruation is a woman's monthly period.Primary amenorrhea is when a girl has not yet started her monthly periods, and she:Has gone through other normal changes that occur during pubertyIs older than 15See also:Menstruation - absentSecondary amenorrheaAlternative NamesPrimary amenorrhea; No periods - primary; Absent periods - primary; Absent menses - primary; Absence of periods - primaryCauses, incidence, and risk factorsMost girls begin menstruating between ages 9 and 18, with an average around 12 years old. Primary amenorrhea typically occurs when a girl is older than 15, if she has undergone other normal changes that occur during puberty. Primary amenorrhea may occur with or without other signs of puberty.Being born with poorly forme