OBJECTIVE: Chemotherapy with irinotecan plus cisplatin has shown promise in chemo-naïve small-cell lung cancer (SCLC) patients. However, irinotecan treatment for relapsed or refractory SCLC has not been adequately evaluated. This phase II study evaluated the appropriate treatment schedule of irinotecan as a single agent. This study was designed to determine the antitumor activity, toxicity, and survival in previously treated SCLC patients. METHODS: Previously treated SCLC patients with at least one platinum-based regimen received irinotecan (100 mg/m2) on days 1 and 8, every 3 weeks, until disease progression. The assessment of the response rate was the primary endpoint. RESULTS: Thirty patients were enrolled, with an objective response rate of 41.3% (95% confidence interval [CI] 25.5-59.3), and a disease control rate of 69%. Median progression-free and overall survival was 4.1 months (95% CI, 2.2-5.4) and 10.4 months (95% CI, 8.1-14), respectively. The grade 3/4 hematological toxicities were neutropenia (36.7%), thrombocytopenia (3.3%), anemia (13.3%), and febrile neutropenia (6.6%). There were no grade 4 nonhematological toxicities. Frequent grade 3 nonhematological toxicities included diarrhea (10%), anorexia (6.6%), and hyponatremia (6.6%). CONCLUSIONS: This phase II study showed a high objective response rate and long survival. Irinotecan monotherapy schedule used was well tolerated, and could be an active treatment option for these patients.