Breast cancer has been reported to confer greater risk for colorectal cancer. In order to estimate the magnitude of this risk, we critically reviewed all studies evaluating the association of breast and colorectal cancer and performed a meta-analysis. The combined results from seven cohort studies demonstrated a weak association between breast cancer and the subsequent risk of colorectal cancer [pooled relative risk (RR) = 1.15; 95% confidence interval (CI) = 0.99-1.31]. Pooled results from five cohort studies showed that the risk of breast cancer after colorectal cancer was similar (pooled RR = 1.10; 95% CI = 1.03-1.17). The combined results from five cross-sectional/case-control studies revealed a positive association between breast cancer and colorectal adenomas (pooled RR = 1.74; 95% CI = 1.27-2.21). Population-based cohort studies, the strongest research design, show essentially no increase in risk of colorectal cancer in women with previous breast cancer. Based upon this evaluation, there appears little justification for special colorectal surveillance of women with previous breast cancer.