The absence of menstruation, or amenorrhea, is a symptom of underlying condition rather than a disease, per se. There are numerous conditions that may cause amenorrhea, which is classified as primary or secondary. Primary amenorrhea refers to a first period that has not occurred in a girl by age of 16. Secondary amenorrhea refers to absent periods in a 3 cycles in a row in a previously menstruating female. The most common cause of amenorrhea is pregnancy, birth control methods, and certain medications. To determine the underlying cause of your amenorrhea, you probably need a pelvic examination and some other tests. Treatment depends on the cause of your amenorrhea and may include lifestyle changes, hormonal or medical therapy. Most underlying conditions that cause amenorrhea are treatable.