A 58-year-old man underwent right lower lobectomy for lung adenocarcinoma in June 1998. Since a high level of tumor marker CEA persisted after surgery, chemotherapy was additionally performed, and the CEA level subsequently normalized. However, the CEA level increased in April 1999, and brain metastasis was found in the left occipital lobe, and the first gammaknife irradiation was performed. Multiple brain metastases were found when CEA increased again in August 1999, and the second gammaknife irradiation was performed. Moreover, brain metastases were found in the left frontal and occipital lobes in February 2000, and the third gammaknife irradiation was performed. CEA normalized thereafter, but increased in February 2001. Brain metastasis was found in the right occipital lobe, and the fourth gammaknife irradiation was performed. CEA has remained within the normal range for about 4 years thereafter. Long-term survival was possible by repeated gammaknife irradiation for brain metastases. Monitoring of CEA played an important role in finding recurrent brain metastasis in this patient.