A 60-year-old man was admitted to our hospital because of the radiologic findings of meningeal carcinomatosis after long-term disease control of epidermal growth factor receptor (EGFR)-mutant non-small cell lung cancer, with cisplatin-based chemotherapy followed by gefitinib. Brain magnetic resonance imaging (MRI) revealed diffuse and linear enhancement on the surface of the midbrain and along the cerebellar folia. In addition, analysis of his cerebrospinal fluid (CSF) showed an increased WBC count and an elevated level of CEA. He presented no symptoms at the time of diagnosis of meningeal carcinomatosis; however, within 2 weeks, neurological symptoms such as disorientation, dysarthria, and ataxic gait became apparent. Since his symptoms seemed to worsen even under further treatment with different cisplatin-based chemotherapy or retreatment with gefitinib, we decided to initiate erlotinib treatment. His symptoms rapidly improved within a week of beginning treatment with erlotinib, and MRI and CSF examinations also showed remarkable improvement of the meningeal carcinomatosis. This case suggests that erlotinib may be effective in some patients with meningeal carcinomatosis previously treated with gefitinib. However, further studies are required to understand the differential efficacy of these drugs.