The detection of silent brain metastasis is becoming increasingly common in patients with non-small cell lung cancer (NSCLC). The aim of this study was to evaluate clinical course, prognostic significance, and treatment efficacy in patients with asymptomatic brain metastasis. A retrospective study of patients with cytologically and histologically diagnosed NSCLC and brain metastasis detected by cranial computed tomography or magnetic resonance imaging was performed. We compared 12 neurologically asymptomatic patients to 69 symptomatic patients and analyzed overall survival, clinical course, and prognostic factors (age, sex, performance status, histologic type, TNM stage, number and size of brain metastases, clinical neurologic status, and treatment of primary tumor and brain metastasis). The strongest favorable prognostic factor was active treatment of both the primary tumor (surgery, chemotherapy and/or thoracic radiotherapy) and brain metastasis (neurosurgery and/or whole brain radiotherapy). Neurologically asymptomatic patients had significantly longer survival times than did symptomatic patients (median survival of 7.5 and 4 months, respectively). Control of clinical neurologic status during follow-up was achieved in a greater proportion of asymptomatic patients (80%) than symptomatic patients (40%). We conclude that it is important to detect brain metastasis in patients with NSCLC before neurologic signs or symptoms develop, as early detection improves prognosis and provides patients with the opportunity of receiving timely and more effective treatment.