What are some reasons for missed periods, other than pregnancy?

Stress can cause you to miss a period, or be late. Starting a new birth control pill can also throw your cycle off. I don't know how old you are, but if you've just started getting your period, it sometimes takes months before you have a regular cycle. Eating disorders can also cause a missed period. When my friend was annorexed she stopped getting her period. Hmm... there might be more reasons. But that all that I can think of.