PURPOSE: Randomized studies have shown that irinotecan (CPT-11) extends survival in metastatic colorectal cancer patients when administered in second-line and when added to fluorouracil (FU) plus leucovorin (LV) in first-line therapy of metastatic colorectal cancer. When this study was initiated, FU plus LV was standard adjuvant treatment for stage III colon cancer. We evaluated the efficacy and safety of weekly bolus CPT-11 plus FU plus LV in the treatment of patients with completely resected stage III colon cancer. METHODS: A total of 1,264 patients were randomly assigned to receive either standard weekly bolus FU plus LV regimen or weekly bolus CPT-11 plus FU plus LV. The primary end points of the study were overall survival (OS) and disease-free survival (DFS). RESULTS: Treatment arms were well-balanced for patient characteristics and prognostic variables. There were no differences in either DFS or OS between the two treatment arms. Toxicity, including lethal toxicity, was significantly higher on the CPT-11 plus FU plus LV arm. CONCLUSION: The addition of CPT-11 to weekly bolus FU plus LV did not result in improvement in DFS or OS in stage III disease, but did increase both lethal and nonlethal toxicity. This trial demonstrates that advances in the treatment of metastatic disease do not necessarily translate into advances in adjuvant treatment, and it reinforces the need for randomized controlled adjuvant studies.