We report the presence of pituitary tissue in a benign ovarian cystic teratoma removed surgically from a 43-year-old woman. The pituitary consisted of non-tumorous neurohypophysis and adenohypophysis containing mainly prolactin (PRL)-immunopositive cells (80 % of cells) and a small PRL-producing adenoma. The ultrastructure of the tumor cells differed significantly from PRL cells in the non-tumorous and adenomatous intrasellar pituitary. It appears that cells differing in ultrastructure from intrasellar pituitary PRL cells can also produce PRL.