PURPOSE: This study aimed to assess the effect of intraoperative blood loss (IBL) on short- and long-term outcomes of colorectal cancer surgery for very elderly patients. METHODS: We acquired the data of consecutive patients aged 80 years or older who underwent elective radical surgery for stage I to III colorectal cancer between January 2003 and December 2007 in 41 institutions. The patients were divided into high and low IBL groups, and the differences in postoperative morbidity and survival between the two groups were primarily assessed. Eleven factors were treated as potential confounders in multivariate analyses. RESULTS: A total of 1554 patients were eligible for this study, with an age range of 80-103 years. Median IBL was 71 ml (interquartile range, 25 to 200 ml), and 412 patients had IBL ≥200 ml. Morbidity was 46% among patients with IBL ≥200 ml, compared with 30 % among those with IBL <200 ml (p < 0.001). Patients with IBL ≥200 ml had worse overall survival rates and recurrence-free survival rates at 1, 3, and 5 years than those with IBL <200 ml. In multivariate analyses, IBL ≥200 ml was identified as an independent risk factor for postoperative adverse events (odds ratio (OR) 1.41, 95% confidence interval (CI) 1.08 to 1.86), overall survival (hazard ratio (HR) 1.34, 95% CI 1.04 to 1.72), and recurrence-free survival (HR 1.29, 95% CI 1.03 to 1.62). CONCLUSION: The degree of IBL is significantly associated with postoperative morbidity and survival in very elderly colorectal cancer patients.