Of the 1548 patients with primary lung cancer who were admitted to our hospital from January 2001 through March 2005, 37 in whom meningeal carciomatosis was diagnosed on cytologic examination of cerebrospinal fluid or magnetic resonance imaging of the brain and spinal cord were studied retrospectively. The most common histologic type was adenocarcinoma, diagnosed in 70% of those patients. The results of cytologic examination of cerebrospinal fluid were positive in 71%. The time from the date of diagnosis of lung cancer to the date of diagnosis of meningeal carcinomatosis ranged from -2 days to 8 years (median, 407 days). Survival from the date of diagnosis of meningeal carcinomatosis ranged from 10 to 392 days (median, 106 days). Treatment for meningeal carcinomatosis was decided on the basis of the patient's general condition and the contorol status of the primary lesion. Radiotherapy, systemic chemotherapy, and palliative therapy were combined. Gefitinib was most often used for chemotherapy after the onset of meningeal carcinomatosis, and 60% of the patients given gefitinib had stable disease. One of these patients (adenocarcinoma) survived for longer than 1 year. Further investigatons are needed to establish standard treatments, including the use of gefitinib, that can improve the quality of life and prolong the survival of patients with meningeal carcinomatosis.