Objectives A cancer lesion sheds tumor cells into the circulating blood as circulating tumor cells (CTCs). Since cluster CTCs have been considered as precursor lesions of metastasis, their clinical implication was investigated in this study according to the preoperative status of cluster CTC detection in surgical cases of clinically early-stage lung cancer. Methods Among 104 surgical patients of early-stage lung cancer, CTCs were extracted from the peripheral blood before surgery using a micro-pore size selection method (ScreenCell®) and diagnosed microscopically. Implications of detecting cluster CTC were assessed according to the prognosis and clinicopathological characteristics. Results The status of CTC detection was not detected in 77 cases (74.0%), single CTC only detection in 7 cases (6.7%), and cluster CTC detected in 20 cases (19.2%). Patients with cluster CTCs exhibited significantly lower recurrence-free survival and overall survival than did patients of other groups. In addition, in hazard ratio analysis, the hazard ratios were independent of other predictors of poor prognosis, and detection of cluster CTCs was associated with predictors of poor prognosis. Conclusion Cluster CTCs were detected in cases where the original lung cancer lesion had clinical predictors of poor prognosis and were independent negative predictors of survival.