Lung cancer is one of the most common cancers and its associated mortality continues to rise in Japan. The lung cancer cure rate is still very low. To improve the survival of patients with lung cancer, well-designed and well-conducted clinical trials are essential. Several Japanese study groups have been conducting clinical trials for lung cancer. However, most randomized phase III studies were conducted by the Japan Clinical Oncology Group (JCOG), the West Japan Thoracic Oncology Group, and pharmaceutical companies supporting temporarily organized groups. In the past decade, the quality of Japanese clinical studies has improved tremendously. The results of JCOG9511 have recently been reported; and demonstrated that treatment with irinotecan/cisplatin significantly improved patient survival in extensive-stage small-cell lung cancer over standard etoposide/cisplatin, with less myelosuppression. A randomized phase II study using gefitinib (ZD1839; Iressa) for non-small-cell lung cancer was also recently reported and showed a high response rate against platinum-refractory lung cancer, especially in adenocarcinoma and in females. A 4-arm multicenter, randomized cooperative phase III study for advanced non-small-cell lung cancer is currently underway.