Amenorrheic athletes have been found to have a lower vertebral bone mineral density (BMD) than matched groups of eumenorrheic athletes. This study reports changes in BMD over a 15.5-month period in athletes who regained menses, athletes who remained amenorrheic, and athletes with regular cycles. The BMD was measured at two sites on the radius and at the lumbar vertebrae (L-1 through L-4), using single- and dual-photon densitometry, respectively. Changes in vertebral BMD were significant for the amenorrheic group (+6.3%), but not for cyclic women (—0.3%). A slight increase in radial density at S-1 and S-2 was not significant for either group. Two athletes who remained amenorrheic during this period continued to lose bone (—3.4%). We conclude that resumption of menses was the primary factor for the significant increase in the vertebral BMD of the formerly amenorrheic athletes.