For lung cancer patients with epidermal growth factor receptor (EGFR) mutations, the advent of EGFR tyrosine kinase inhibitors (TKIs) has prolonged survival rates. Even though disease sites have been well controlled by EGFR-TKIs, some patients develop carcinomatous meningitis, which reduces their quality of life drastically. Although multidisciplinary approaches have improved patient survival and quality of life, the outcomes are not yet satisfactory. We report the case of a 54-year-old Japanese woman diagnosed with leptomeningeal metastases (LM) from a lung adenocarcinoma harboring an EGFR exon 21 L858R point mutation. She was treated with gefitinib for 2 months, and symptoms of LM emerged during the treatment period. Although the treatment was switched to erlotinib, disturbance of consciousness worsened because of progressive hydrocephalus. Because all extracranial lesions remained responsive to treatment, and the exon 20 T790M point mutation was not detected in cerebrospinal fluid, we placed a ventriculoperitoneal shunt. The patient's disturbed consciousness improved dramatically after the shunt was placed; however, the optic and auditory nerve impairments due to direct invasion of LM lesions into nerve canals persisted. Administration of bevacizumab subsequent to whole-brain radiotherapy reduced the cranial nerve impairment, and the patient survived for 10 months. In conclusion, a combination of erlotinib and ventriculoperitoneal shunt was effective for hydrocephalus, and the immediate administration of additional therapies, including bevacizumab and radiation therapy, was useful in a patient suffering from LM.