In a prospective multicenter trial, 279 patients with metastatic colorectal cancer who had failed 5-fluorouracil therapy were randomized 2:1 to receive either best supportive care (BSC) plus treatment with the topoisomerase I inhibitor, irinotecan (CPT-11; Rhône-Poulenc Rorer, Antony, France), at a dose of 350 mg/m2 every 3 weeks or BSC alone. Overall survival, the primary end point of the study, was significantly improved in patients receiving the irinotecan treatment. Only 14% of patients receiving BSC alone were alive at 1 year compared with 36% in the irinotecan group. After adjustment for prognostic factors such as performance status, the difference in survival favoring irinotecan remained highly significant (P = .001). The benefit of irinotecan was also observed through significantly longer survival without performance status deterioration, longer survival without more than 5% weight loss, and longer duration of pain-free survival. Appreciable deterioration in global quality of life (50% reduction from baseline) occurred significantly later in the irinotecan-treated patients than in the controls. Additionally, quality of life analyses of all symptoms, except diarrhea, mean scores were significantly in favor of patients assigned to irinotecan treatment than those assigned to BSC. This is the first time that the benefit of second-line chemotherapy has been demonstrated by a randomized controlled trial in advanced colorectal cancer.