The purpose of the study was to investigate the seasonal relationship of athletic amenorrhea and body composition in elite, adolescent, cross-country runners. The participants consisted of 28 female adolescent cross-country runners (mean age ± SD = 15.4 ± 1.5 years); 17 eumenorrheics and 11 amenorrheics. The participants’ body composition was measured pre- and postseason using dual-energy X-ray Absorptiometer (DXA). The eumenorrheics’ postseason BMD was significantly greater than the amenorrheics’ postseason BMD (F(1,54) = 16.22, p < .05, partial η² = .231). The eumenorrheics’ postseason bodyweight (F(1,54) = 7.65, p < .05, partial η² = .124), BF (F(1,54) = 8.56, p < .05, partial η² = .137), and BMC (F(1,54) = 8.52, p < .05, partial η² = .136) were significantly greater than the amenorrheic subgroup. There was also a significant seasonal increase in BMD (t(27) = –4.01, p < .05) for the overall group and the eumenorrheic subgroup (t(16) = –3.90, p < .05). Bodyweight best predicted BMD (F(1,26) = 46.434, p < .05, R² = .641). In the study, athletic amenorrhea was highly associated with lower levels of BMD in the participants, and crosscountry running was highly associated with increased BMD.