Background: Use of calcium channel blockers (CCBs) has been associated with increased risk of breast cancer in some, but not all, studies. Differences in reported associations from prior studies may be due, in part, to inadequate control of confounding factors.Methods: Participants were 28,561 postmenopausal women from the Women's Health Initiative who reported use of either CCBs or other antihypertensive medications (AHMs) at baseline; 1,402 incident breast cancer cases were diagnosed during 12 years of follow-up. Adjusted Cox regression models were used to estimate HRs and 95% confidence intervals (CI) for the associations between CCB use relative to other AHM use and breast cancer risk.Results: Use of CCBs was not associated with breast cancer risk (HR, 1.06; 95% CI, 0.94-1.20) relative to use of other AHMs. Associations approximated the null value when CCBs were considered by duration of use, length of action, or drug class.Conclusions: We provide additional evidence that CCBs do not influence breast cancer risk in postmenopausal women.Impact: The results from this study, which includes strong control for potential confounding factors, cast doubt on increases in risk with CCBs. Cancer Epidemiol Biomarkers Prev; 26(8); 1345-8. (c)2017 AACR.