It is important to determine the bone mass in normal premenopausal women because increasing numbers of conditions have been identified that result in premenopausal osteoporosis. The relationship between age and bone density was evaluated in 57 carefully characterized normal, premenopausal women using both single energy quantitative computed tomography (SEQCT) and dual energy (DEQCT). The mean bone density measurements were 172 mg/ml K2HPO4 SEQCT and 185 DEQCT. Bone density showed no statistically significant decline between age 18 and age 44. Single- and dual-energy data were highly correlated with each other (r = 0.89), and dual energy appeared to confer no advantage. There was an inverse relation between density and age of menarche. Bone density did not correlate with ideal body weight, percentage fat, or subcutaneous fat area.