A 25-year-old female presented with pituitary prolactinoma associated with polycystic ovarian disease and amenorrhea. After trans-sphenoidal adenomectomy, the serum prolactin level returned to normal. Postoperative ultrasonography revealed resolution of the polycystic ovary. Regular menses recommenced 2 months after surgery. Our experience suggests that pituitary prolactinoma may be a cause of polycystic ovarian disease.