BACKGROUND: Although lack of exercise is well known to be a risk factor of osteoporosis, it is unclear whether weight-bearing exercise has different effects on bone mineral density compared to non weight-bearing exercise, and the amount of exercise needed to prevent osteoporosis is not clearly defined. This study was performed to clarify the relations between the type and the amount of exercise with BMD. METHODS: This was a cross-sectional study of 3,661 women who had undertaken health screening including BMD measurement at Health Promotion Center of SNUH between May 1997 and March 1999. Information on sociodemographic characteristics, menarche, childbirth andexercise were gathered by means of self-reported questionnaire, and BMD was measured using DEXA. RESULTS: The number of women with lumbar osteoporosis were 601 (16.4%) and femoral neck osteoporosis 372 (10.2%). Lumbar osteoporosis occurred more frequently with increasing age and age at menarche, and in menopausal women, but less frequently with increasing fat-free mass in multiple logistic regression analysis. When adjusted for age, age at menarche, menopause and fat-free mass, lumbar osteoporosis was less common in women who exercised, but the type and the amount of exercise had no bearing. Especially, lumbar osteoporosis was least common in women engaging in moderate amount of exercise. Femoral neck osteoporosis decreased significantly only in weight-bearing exercise group and in women engaging in high amount of exercise. CONCLUSION: The results of this study suggest that lumbar osteoporosis can be prevented through exercise regardless of its type and amount, and high amount or weight- bearing exercise is most effective to prevent femoral neck osteoporosis.