Some pituitary adenomas seem to be related to bone loss. It is unknown what kinds of pituitary adenomas affect bone mass. We attempted to determine what kinds of pituitary adenomas caused osteoporosis, and whether hormonal disturbance in pituitary adenoma patients affected bone mass. This study included 53 surgical patients (39 women of premenopausal age and 14 men) aged 21 to 62 years. We measured vertebral bone mineral density (BMD); various bone metabolic parameters, such as serum calcium, phosphorus, alkaline phosphatase, and blood urea nitrogen, parathormone, vitamin D, vitamin K, and hormonal activity in the anterior lobe of the pituitary gland. Comparisons were made of the mean Z scores (the ratio to the mean BMD of age-matched healthy Japanese women and men) among patient groups and controls. Compared with the female controls, the mean Z score was significantly higher in the women with acromegalic adenoma and significantly lower in those with adrenocorticotrophic hormone (ACTH)-secreting adenoma. In male patients, the mean Z scores were significantly decreased in prolactin-secreting adenoma and nonfunctioning adenoma, compared with that in normal controls. Acromegalic adenoma contributes significantly to vertebral bone mass acquisition, although ACTH adenoma may carry a significant risk of osteoporosis in female patients. Male patients with prolactin-secreting and nonfunctioning adenoma have a significant risk of bone decrease.