In this cross-sectional study, 91 healthy premenopausal women aged 20-39 years were investigated to determine the effect of physical activities during their teenage years on their current bone mineral densities (BMD). We measured whole-body BMD (WBMD), lumbar BMD (LBMD), and radial BMD (RBMD) with dual energy X-ray absorptiometry (DXA). Using a questionnaire, we asked the women about their physical activities during junior and senior high school and at present. We also asked about their current nutritional status and past and current milk intake. After adjusting for age, body mass index (BMI), current total calorie and calcium (Ca) intake, and milk intake when they were teenagers and at present, we determined that subjects who exercised during extracurricular activities at each of the three periods (during junior and senior high school and at present) had significantly higher WBMD and LBMD (P <0.01, respectively) than did those who did not exercise at those times. Subjects who played high-impact sports at each period had significantly higher WBMD and LBMD than did subjects who played low-impact sports (P <0.05, respectively). Subjects who had exercised regularly from their teenage years to the present had significantly higher BMD at all sites than BMD in other subjects after adjusting for the potential confounders described above (P <0.05, respectively). Our data suggest that continuous exercise beginning in junior high school, especially high-impact sports, may be associated with greater current bone mass. It is important to incorporate adequate exercise beginning in the teenage years to lower one's future risk for osteoporosis.