A Phase III study was started in Japan to evaluate the non-inferiority in overall survival of segmentectomy compared with lobectomy in patients with small-sized (diameter ≤2 cm) peripheral non-small cell lung cancer, excluding radiologically determined non-invasive cancer. This study began in August 2009, and a total of 1100 patients will be accrued from 71 institutions within 3 years. The primary endpoint is overall survival. The secondary endpoints are post-operative respiratory function, relapse-free survival, proportion of local recurrence, adverse events, proportion of patients who complete segmentectomy, duration of hospitalization, duration of chest tube placement, operation time, blood loss and number of auto-sutures used. This study is one of the first intergroup studies in Japan between the Japan Clinical Oncology Group and the West Japan Oncology Group.