BACKGROUND: The purpose of this study was to assess the efficacy and toxicity of biweekly irinotecan plus 5-fluorouracil (FU) and leucovorin (LV) in patients with relapsed or metastatic colorectal cancer. MATERIALS AND METHODS: Between March 2002 and May 2004, 24 patients with histologically confirmed relapsed or metastatic colorectal cancer were enrolled in this study. One chemotherapy cycle consisted of irinotecan 180 mg/m(2) on days 1 and 15; 5-FU 400 mg/m(2) bolus IV with 600 mg/m(2) by a 22 hour intravenous infusion on days 1, 2, 15 and 16; and leucovorin 20 mg/m(2) on days 1, 2, 15 and 16, every 4 weeks. RESULTS: The median age of the 24 was 57.5 years (range, 38 approximately 69). Their metastatic sites included: the liver (62.5%), lung (20.8%), peritoneum (16.7%), lymph node (12.5%), ovary (8.3%) and pelvis/vagina (8.3%). Twenty-two patients were evaluable for a response. Six and 7 patients achieved partial responses and stable diseases, respectively. The overall response rate was 27.3% (95% Confidence interval; 10.3 approximately 44.5%). The median follow-up duration for surviving patients was 14.7 months (range, 1.7 approximately 26.5). Median overall survival (OS) and 1-year OS rates were 19 months and 86.3%, respectively. Median response duration and median progression free survival were 7.47 and 5.57 months, respectively. A total of 83 cycles (median 4 cycles) were administered. The main non-hematologic toxicities were nausea/vomiting (44.5%/18.1%) and diarrhea (8.4%). The most common hematologic toxicity was NCI grade I/II anemia (31.3%) and grade I/II neutropenia was 10.8%. There was no life-threatening toxicity. CONCLUSION: The results suggested that irinotecan, 5-FU and leucovorin combination chemotherapy in a biweekly schedule is a practical and tolerable treatment option in patients with advanced colorectal cancer.