The implantation of malignant cells along the needle tract is an extremely rare complication after a percutaneous fine-needle aspiration biopsy(FNAB). However, it is very serious and may result in a change in the prognosis of lung cancer, especially in the curable early stage(T1-2,N0,M0). Recently, we experienced two cases of such complications. A 43 years old female underwent a fine needle aspiration biopsy and a right middle lobectomy with adjuvant chemotherapy due to an adenocarcinoma(T2N0M0). Two years later, a new tumor developed at the site of the needle aspiraton biopsy. It had the same pathological findings as the previous lung cancer. Therefore, it was concluded to be an implantation metastasis, and she was treated successfully by a right pneumonectomy and a resection of the chest wall mass with adjuvant radiotherapy. In another case, a 62 years old man was diagnosed with squamous cell lung cancer by a fine needle aspiration biopsy and underwent a right upper lobectomy(T2N0M0) with adjuvant chemotherapy. eight months later, a protruding chest wall mass developed at the aspiration site. It showed the same pathological findings as the previous lung cancer. Consequently, a total excision of the mass with adjuvant radiotherapy was done. Two years after the second operation, although the right lung was intact, a metachronous squamous cell lung cancer was found at the left lower lobe. The two patients were still alive 15 and 37months after thenresection of the chest wall mass, respectively.