Among 1372 lung cancer patients without brain metastasis that underwent resection of lung cancer at our center from 2001 to 2007, brain metastases developed in 72 patients (5.2%) during their hospital course. We hypothesized that there were micro-metastases in the brain at the time of lung surgery in these patients, even though there were no detectable brain metastases on the MRI. The purpose of this study was to evaluate the growth rates of metastatic brain tumors in this unique subset of patients, and to compare the findings with our previous study that calculated the growth rate of brain metastases during chemotherapy. Among 72 patients, 23 with cystic or hemorrhagic metastases were excluded. Seventy-six metastatic brain tumors in 49 patients were reviewed. Twenty-five patients underwent adjuvant or neoadjuvant chemotherapy; however, for the rest of the patients, chemotherapy was not added after lung cancer surgery. The tumor volume was determined using V-works software (v. 4.0) (Cybermed, Seoul, Korea) and T1 gadolinium enhanced MR images. The overall median tumor growth rate was 11.7 mm³/day (interquartile range, 4.9-26.8). There were no statistically significant differences in the tumor growth among the lung cancer stages and the growth rate was similar regardless of the use of chemotherapy. The growth rate reported in this study shows consistency with that of our previous report (12.1 mm³/day). These findings may help optimize patient management during follow up.