In a retrospective study data were collected from 644 patients with cancer of the colon or rectum undergoing curative surgery with extended lymphadenectomy to evaluate a possible effect of blood transfusion, given perioperatively, on tumor recurrence and patient survival. Univariate analysis showed depth of bowel wall invasion, number and level of lymph node metastases to be of highly significant prognostic factors. After 5 years the overall recurrence rate was 16.6% for the non-transfused (n = 223) and 26.1% for the transfused (n = 421; p < .01) patients, and survival rates showed borderline significance favoring the non-transfused patients (90.5% vs. 80.0% after 5 years; p < 0.05). However, after stratification for the prognostically important factors, in a multivariate analysis a possible detrimental effect of perioperative blood transfusions could not be demonstrated.