A 70-year-old woman underwent radical nephrectomy for right renal cell carcinoma and received prophylactic interferon-alpha (rHuIFN-alpha) administration for one year. Followup computerized tomography scan showed a small nodule in the right lung 39 months postoperatively. Pulmonary nodules had become multiple and increased in size (6 mm) at 53 months. To examine the pulmonary lesions, histopathologically thoracoscopic biopsy of the right pulmonary nodule was performed and the diagnosis of metastatic renal cell carcinoma was confirmed. Because of its minimal invasiveness, thoracoscopic biopsy may be indicated in selected cases.