Background: Knowing the status of the internal mammary lymph (IML) nodes is important for accurate staging and appropriate selection of subsequent treatment in breast cancer. We conducted a meta-analysis to clarify the rate of IML node metastasis in breast cancer patients and discussed the importance of this finding. Methods: We retrieved articles from the literature that reported positive rates of IML node metastasis in breast cancer patients. The quality of the selected articles was assessed using the ‘Methodological Index for Non-Randomized Studies'. The heterogeneity was tested, and publication bias was assessed using a funnel plot. Finally, the positive rate of IML node metastasis in breast cancer patients was calculated using the random-effects model. Results:15 articles met the inclusion criteria and a total of 4,248 patients were included in the analysis. Heterogeneity across the studies was statistically significant (p = 0.014); thus, the random-effects model was used and the calculated positive rate of IML node metastasis was 23% (95% confidence interval (CI), 0.21-0.25). Conclusions: Approximately 23% of the breast cancer patients had IML node metastases, for which the prognosis is generally poor. Accurate staging and integrated treatment are necessary to improve the survival of these patients.