Abstract: Objective:To investigate the effectiveness of immunoFISH technology in detecting tumor cells in cerebrospinal fluid (CSF) for adjuvant diagnosis of meningeal metastasis from lung cancer. Methods:Circulating tumor cells (CTCs) were detected by im -munoFISH technology in CSF samples from16patients with meningeal metastasis from lung cancer and 8 patients with non-tumorous brain diseases. Meningeal metastasis from lung cancer was diagnosed on the basis of neurological symptoms and confirmed by en-hanced magnetic resonance imaging and CSF cytological examination. Results: The number of CTCs was significantly greater in pa-tients with meningeal metastasis from lung cancer than in those with non- tumorous brain diseases (P<0.01). The critical point of the maximum correct diagnosis index (Youden index) was regarded as the judging criterion for the positive tumor cells in CSF based on the receiver operating characteristic curve. When one tumor cell existed in 7.5 mL of CSF, the area under the curve was0.875, and the 95% confidence interval ranged from 0.705 to 1.000. The diagnostic sensitivity, specificity, effectiveness, positive predictive values, and neg -ative predictive values were 75.0%,100.0%,83.3%,100.0%, and 66.7%, respectively.Conclusion:ImmunoFISH technology provides great significance in detecting CTCs in CSF to diagnose meningeal metastasis from lung cancer.