Objectives：The object of this study is to evaluate the incidence, survival and the prognostic factors in patients with leptomeningeal metastasis from non-small cell lung cancer. Methods：The study included fifty-five consecutive patients diagnosed with brain parenchymal metastasis on magnetic resonance image (MRI) clinically from non-small cell lung cancer between July 2010 and February 2011. All the patients underwent lumbar puncture for cerebrospinal fluid examination including cytology examination with cytokeratine immunostain. If the patients showed positive in cerebrospinal cytology or leptomeningeal enhancement on T1 weighted gadolinium enhanced MRI, whole spine MRI with gadolinium enhancement was also taken for evaluation of spinal disease. For evaluation of prognostic factors, we investigated the patient`s age, interval from the time of diagnosis of systemic disease to the time of diagnosis of leptomeningeal metastasis, interval from the time of diagnosis of parenchymal metastasis to the time of diagnosis of leptomeningeal metastasis, performance status of the patients, and following treatment modality after diagnosis of leptomeningeal metastasis. Result：In eleven (20%) of the fifty-five patients, the diagnosis of leptomeningeal metastasis was made on the basis of MRI findings and the results from cerebrospinal fluid cytology. Among those eleven patients, eight (72.7%) had positive cerebrospinal fluid cytology at the time of initial examination. Eight of the eleven patients underwent an operation for intraventricular catheter and reservoir placement in order to receive intraventricular chemotherapy. In six (75%) of the eight intraventricular chemotherapy patients, the negative conversion of cerebrospinal fluid cytology was achieved during induction chemotherapy of four weeks. The overall median survival for the eleven patients after the diagnosis of leptomeningeal metastasis and the eight subsequent intraventricular chemotherapy patients was 62 days (95% confidence interval 27.4-96.6). The most possible prognostic factor was the intervals from primary disease to leptomeningeal metastasis (p=0.071). Conclusion：In this study, we found that relatively high proportion of the patients of non-small cell lung cancer with parenchymal metastases were co-morbided by leptomeningeal metastases, and revealed that the interval from primary disease to leptomeningeal metastasis could be an important factor for survival. However, further well-designed investigations, with larger sample sizes, must be conducted to evaluate other prognostic factors as well as new drugs, and to define the optimal treatment combinations and route.