The results of transsphenoidal microsurgery in treating 37 patients (30 women and seven men) with pituitary tumors associated with hyperprolactinemia are presented. Immediate (10-day) postoperative fasting prolactin levels were normal (less than 25 ng/ml) in 19 of 26 patients whose preoperative prolactin level was less than 200 ng/ml, and in only three of 11 patients in whom preoperative prolactin was greater than 200 ng/ml. Twelve of 13 patients with normal preoperative pituitary-target organ function maintained normal axes postoperatively. Thirteen other patients had preoperative deficiencies in one or more pituitary-target organ axes. Postoperatively, in these latter 13 patients, a pituitary-target organ axis that was deficient preoperatively returned to normal in six cases; there was no change in five, and there was impairment in another axis in four instances. Although gross total tumor removal was believed to be complete in 35 of 37 patients, serial postoperative prolactin determinations in four of these 35 patients indicate tumor regrowth. The authors conclude that transsphenoidal microsurgery is currently the operative procedure of choice for the majority of pituitary tumors associated with hyperprolactinemia.