© 2014 Hirashima et al. Although active Mycobacterium tuberculosis (MTB) or Mycobacterium Kansasii (MK) infection could be present in patients with metastatic colorectal cancer (m-CRC), no study is available on the clinical courses and chemotherapy outcomes of these patients. The present study therefore aimed to retrospectively examine whether m-CRC patients with and without active MTB or MK infection could receive cancer chemotherapy similarly. Methods: This study enrolled 30 m-CRC patients who received first-line chemotherapy between January 31, 2006 and January 31, 2013 at our institution, The clinical courses and tumor response of those with and without active MTB or MK infection were examined and compared. Results: Of 30 m-CRC patients, 6 had active MTB infection, 1 with active MK and the other 23 had neither MTB nor MK. No significant demographic differences were observed between patients with MTB or MK and those without. Chemotherapy response rates of all patients, those with MTB or MK, and those without were 40.0%, 28.6% and 43.5%, respectively. Among patients with MTB or MK, 1 treated with bevacizumab experienced grade-3 hemoptysis while others did not report any severe toxicity. Median survival time of all studied patients, those with MTB or MK, and those without was 26.3, 36.7 and 22.6 months, respectively. No significant difference in overall survival was observed between patients with MTB or MK and those without. Multivariate analysis revealed that performance status and liver metastasis were significant prognostic factors of overall survival (P = 0.004 and 0.030, respectively), whereas other factors, including MTB or MK infection, were not. In our study, all 7 patients with MTB or MK did not experience infection relapse during or after cancer chemotherapy. Conclusions: Our results indicate that m-CRC patients with MTB or MK should be able to safely and effectively continue cancer chemotherapy to subsequently achieve comparable survival duration to those without the infection if they receive proper MTB or MK treatment.