Thank you for your question. A dermoid cyst (also called a mature teratoma) is a common type of benign growth on the ovary. It’s different from other ovarian cysts such as a Follicular or Corpus Luteum because a dermoid cyst doesn’t affect your hormones. These cysts are usually not harmful but can result in pain if there is torsion of the ovary (twisting of the ovary). Having a dermoid shouldn’t affect your periods. Sometimes when a girl is stressed about surgery, hormone levels may fall and the result is a period. If you haven’t had your period for years, you should see your primary care provider (PCP) and figure out what is causing the problem.