Context: The association between bone mineral density (BMD) and breast arterial calcification (BAC) remains poorly understood and controversial. Objective: The objective of this article is to examine the association between BMD and BAC in a large cohort of postmenopausal women undergoing routine mammography. Design: A cross-sectional analysis of baseline data from a multiethnic cohort was performed. Setting: The setting for this analysis is an integrated health care delivery system in Northern California in the United States. Patients: A total of 1273 women age 60 to 79 years (mean age, 67 years) were recruited within 12 months of screening mammography. Main outcome measure: A BAC score (mg) was obtained from digital mammograms using a novel densitometry method. BAC presence was defined as a BAC score greater than 0 mg, and severe BAC as a BAC score greater than 20 mg. Results: Overall, 53% of women had osteopenia and 2] % had osteoporosis. The prevalence of RAC greater than 0 mg was 29%, 30%, and 29% among women with normal BMD, osteopenia, and osteoporosis, respectively (P= 0.98). The prevalence of BAC greater than 20 mg was 5%, 3%, and 5% among women with normal BMD, osteopenia and osteoporosis, respectively (P= .65). The odds ratios (ORs) of BAC greater than 0 mg vs BAC = 0 mg after multivariable adjustment were 1.09 (95% CI, 0.81-1.48; P= .54) for osteopenia and 0.99 (95% CI, 0.69-1.48; P= .98) for osteoporosis. The adjusted ORs for BAC greater than 20 mg vs BAC 20 mg or less were 1.03 (95% CI, 0.52-2.01; P= .93) for osteopenia and 1.89 (95 CI, 0.81-4.47; P= .14) for osteoporosis. Conclusion: Our findings do not support an association of either osteopenia or osteoporosis with BAC presence or severity among postmenopausal women. (C) Endocrine Society 2019.