From the Green words "teratos" or "monster" and "onkoma" or "swelling". These lesions are derived from multiple germ layers with the ability to differentiate into one, two or all three germ cell layers. Most are found in the first two decades of life with a peak incidence in the reproductive years. 85 to 90 percent are benign and are considered mature cystic teratomas. 15 to 20 % of the benign teratomas are bilateral. The remaining 10 to 15 % are immature. 1 to 2% of mature teratomas will display malignant degeneration after the age of 40, with the most common malignancy being squamous cell carcinoma.

The cystic component of the teratoma is usually incapsulated with a smooth capsule and will very in size from microscopic to a large mass weighing up to 15 pounds. The cyst is usually of sebaceous material. Teeth and bone can be seen in a solid prominence called Rokitansky's protuberance which is at the point of contact with the residual ovarian tissue.