Amenorrhea
Internet URL
http://www.mayoclinic.com/health/amenorrhea/DS00581 
Sponsoring Agency
Mayo Foundation for Medical Education and Research
Description
Amenorrhea — the absence of menstruation — can happen during puberty or later in life. Primary amenorrhea describes a condition in which you haven't had any menstrual periods by age 16. Secondary amenorrhea occurs when you were previously menstruating but then stopped having periods. Pregnancy may be your first thought if you miss a period, but there are many reasons why you might not be menstruating regularly.