Few longitudinal studies have investigated the effects of amenorrhea and amenorrhea plus exercise on bone mineral density (BMD) of young women. We carried out a 2-yr comparison of dancers and nondancers, both amenorrheic and normal, that investigated the role of hypothalamic amenorrhea on bone in this context. We studied 111 subjects (mean age, 22.4 +/- 4.6 yr; age of menarche, 14.1 +/- 2.2 yr), including 54 dancers, 22 with hypothalamic amenorrhea, and 57 nondancers, 22 with hypothalamic amenorrhea. Detailed hormonal and nutritional data were obtained in all groups to determine possible causal relationship to osteoporosis. The amenorrheic groups, dancers and nondancers, both showed reduced BMD in the spine, wrist, and foot, which remained below controls throughout the 2 yr. Only amenorrheic dancers showed significant changes in spine BMD (12.1%; P < 0.05) but still remained below controls, and within this subgroup, only those with delayed menarche showed a significant increase. The seven amenorrheic subjects (three dancers and four nondancers) who resumed menses during the study showed an increase in spine and wrist BMD (17%; P < 0.001) without achieving normalization. Delayed menarche was the only variable that predicted stress fractures (P < 0.005), which we used as a measure of bone functional strength. Analysis of dieting and nutritional patterns showed higher incidence of dieting behavior in this group, as manifested by higher Eating Attitudes Test scores (16.3 +/- 2.00 vs. 11.5 +/- 1.45; P < 0.05) and higher fiber intakes (30.7 +/- 3.00 vs. 17.5 +/- 2.01 g/24 h; P < 0.001). We concluded that low bone mass occurs in young women with amenorrhea and delayed menarche, both exercisers and nonexercisers. Crucial bone mass accretion may be compromised by their reproductive and nutritional health.