Germ cells are found in the male and female reproductive systems. Ovarian germ cell tumours are tumours found in the cells that produce a woman's egg in the ovaries. There are different types of ovarian germ cell tumours and they are named after the types of cells from which the tumour develops. Dysgerminomas germ cell tumours occur the most often and they often affect both of the ovaries. Non-dysgerminomatous germ cell tumours are known as mixed tumours because they contain more than one type of cell. They usually affect only one ovary.