PURPOSE: To assess the association between mammographically detected breast arterial calcification (BAC) and coronary artery disease (CAD) and diabetes mellitus (DM). MATERIALS AND METHODS: The records of 182 women (aged 39-92 years) who underwent both mammography and coronary arteriography were retrospectively reviewed to determine BAC, CAD, and DM status. RESULTS: Far women aged less than 59 years (under-59 group) (n = 54), nearly all women with BAC (n = 8) had CAD (n = 7) and also had DM (n = 6). For this group, the positive predictive value of BAC for CAD was 0.88 and the negative predictive value was 0.65 (chi(2) = 7.7, P < .05). DM was a confounding variable. The positive predictive value of DM for CAD increased from 0.62 when BAC was absent to 1.00 when BAC was present (standard error of difference, .22; P < .10). No significant association between BAC and CAD was found for women aged 59 years and older (n = 128). CONCLUSION: BAC in women aged less than 59 years may indicate an additional risk factor for CAD, particularly in diabetic patients.