Our purpose was to determine the relationship of diet, exercise, and amenorrhea with bone mineral status in trained young women. Bone mineral density of the lumbar spine was significantly lower in amenorrheic compared to normally menstruating runners. Circulating estradiol was also significantly lower. No significant differences between the two groups were found in body composition, maximum aerobic power, or amount of training per week. A 3-day dietary record showed that the amenorrheic women reported a significantly lower daily energy intake, but no difference in the calcium intake. Protein intake was less than the US Recommended Dietary Allowance in 82% of amenorrheic women and 35% of eumenorrheic women. Abnormal eating behaviors may be associated with the development of amenorrhea. Our results show that when weight-bearing exercise and a low energy intake are associated with amenorrhea, the accretion of a large bone mass in young trained women is not favored.