To determine whether women with PRL-secreting pituitary tumors have similar decreases in cortical and trabecular bone and to determine whether bone loss associated with hyperprolactinemia is reversible, we measured forearm and vertebral bone mineral in normal women and in amenorrheic women with treated and untreated hyperprolactinemia. The mean spinal bone mineral content in hyperprolactinemic women [130 +/- 23 (+/- SD) mg/mL] was 25% lower than that in normal women (167 +/- 28 mg/mL), while the mean forearm bone mineral content (0.71 +/- 0.04 g/cm2) was similar to that in normal women (0.73 +/- 0.05 g/cm2). Women with normal serum PRL levels and regular menses after transsphenoidal surgery had slightly higher mean spinal bone mineral content (149 +/- 28 mg/mL) than women who remained amenorrheic after surgery (129 +/- 19 mg/mL), but the mean value in the cured women remained significantly lower than that in normal women. In contrast, women who had undergone successful transsphenoidal pituitary surgery had mean forearm bone mineral comparable to that in normal women. There was no correlation between vertebral and radial bone mineral in hyperprolactinemic women and no correlation between bone mineral and serum PRL, serum estradiol, or duration of amenorrhea when age was taken into account. These findings suggest that hyperprolactinemia and/or decreased gonadal function in women with PRL-secreting pituitary tumors are associated with more prominent effects on trabecular bone in the spine than on cortical bone in the wrist. In addition, the abnormal spinal bone mineral content after successful treatment suggest that normalization of estradiol and PRL secretion is not sufficient to restore bone mineral content to normal, although it may be stabilized.