BACKGROUND: Several studies have demonstrated that mammographic dense breast is related to the risk of breast cancer and is associated with decreased mammographic sensitivity and specificity. In contrast, studies concerning women with dense breast are virtually non-existent. This study was conducted to evaluate the relationship between mammographic dense breast and other risk factors of breast cancer, and to make a plan for individualized strategies in high risk populations. METHODS: The study subjects were 565 women, aged 20~70 years, who had a screening mammogram from April 2005 to August 2005 at a health promotion center. Data of demographic factors, breast caner risk factors and menstrual status were collected by the self-administered questionnaire. Mammographic breast density was classified according to the American College of Radiology Breast Imaging Reporting and Data System (BI-RADS) fours categories, as measured by the proportion of glandular tissues within the total breast tissue. RESULTS: By BI-RADS categories, 'entirely fat' were 46, 'scattered fibroglandular' were 96, 'heterogenous dense' were 332 and 'extremely dense' were 91 (16.1%). Univariate analysis showed that age, occupation, education level, body mass index, age at menarche, parity, breast feeding, menopausal status and triglyceride had significantly related to dense breast (P<0.05). In the multivariate logistic analysis, only low body mass index (P<0.001), low parity (P=0.009, 0.038) and premenopausal status (P=0.001) were significantly associated with dense breast. CONCLUSION: In Korean women, dense breast was significantly associated with low body mass index, low parity and premenopausal status. Therefore, if women with dense breast have these risk factors, they need to be managed more intensively with regular screening, breast sonogram, and lifestyle modification.