This study was performed to obtain a comprehensive overview of the benefits and risks of second-line irinotecan monotherapy for advanced colorectal cancer. The literature was systematically reviewed to identify phase II and phase III trials that investigated the effect of second-line monotherapy with irinotecan. Thirty studies were included in this review: 25 phase II studies including 32 samples and five phase III studies including six samples. A disease control rate of greater than or equal to 50% was found in 23 out of 32 phase II samples, and one out of two phase III samples that reported disease control rate. Median time to progression was 2.7-6.0 months in phase II samples and 3.0-4.3 months in phase III samples. Median overall survival ranged from 6.6 to 16.1 months in phase II samples and 9.1-10.8 months in phase III samples. The most important severe adverse event in both phase II and phase III trials was diarrhea (5-39 and 15-36%, respectively), followed by nausea (1-24 and 5-14%), vomiting (2-22 and 6-14%), and asthenia (0-31 and 4-21%). Treatment-related mortality was 0-2% in phase II samples and 0-5% in phase III samples. Quality-of-life scores in phase II studies were associated with tumor response. In phase III studies, the quality of life while on treatment with irinotecan was similar to that of 5-fluorouracil, but better than supportive care alone. The quality of life on the weekly schedule was similar to the 3-weekly schedule. This study provides a comprehensive overview of the benefits and risks of second-line irinotecan. In general, second-line treatment with irinotecan is beneficial to patients.