Leptomeningeal carcinomatosis (LM) is a clinically important complication of adenocarcinoma of the lung. However, because it is difficult to diagnose, LM is rarely reported. We report two cases in which the initial signs and symptoms were headache, seizure attack, and nuchal rigidity. The first case was suspected to be tuberculosis meningitis on the basis of shared symptoms, signs, and laboratory data from cerebrospinal fluid analysis. The diagnoses of both cases were established by cytology of the cerebrospinal fluid and supported by neuroimaging. However, the prognosis for LM is poor despite aggressive present-day treatment.