Leptomeningeal carcinomatosis is usually diagnosed in 5% to 7% of the malingnant tumors, which lung cáncer is the most commun cause in all its hystological types. We present a clincal case, where the patient complaints of head ache, blurred visión and where idiopatic hydrocephalus was diagnosed. Months after de Ventricular peritoneal shunt was placed, the patient comes back with lost of weigth, astenia, dysphagia and sensorial disturbances. Autopsy revealed a lung adenocarcinoma with micrometastasis to the brain and leptomeningeal carcinomatosis.