A 51-year-old female presented with left facial palsy. She had adenocarcinoma of the lung with multiple brain metastases. The primary tumor regressed after treatment with gefitinib, however, neurological symptoms progressed rapidly because of meningeal carcinomatosis, when a deletion mutation in exon 19 of the epidermal growth factor receptor in cells from her cerebrospinal fluid was detected. After performing lumbo-peritoneal shunting, her symptoms improved dramatically and she had been well without peritoneal dissemination for 15 months, continuing gefitinib treatment. Finally, she died 18 months after lumbo-peritoneal shunting. A T790M acquired-resistance mutation in exon 20 of the epidermal growth factor receptor was found from her mesenteric lymph nodes and cerebrospinal fluid at autopsy. A lumbo-peritoneal shunt might be considered for meningeal carcinomatosis refractory to gefitinib treatment without an emergence of a T790M mutation.