Paraneoplastic limbic encephalitis (PLE) is a disorder characterized by severe cognitive dysfunction and seizures. It is usually associated with small cell lung carcinoma. Diagnosis is difficult because clinical markers are often lacking, and symptoms usually precede the diagnosis of cancer. Serological detection of antineuronal antibodies can be useful. We describe a patient with symptoms of limbic encephalitis, negative for paraneoplastic antibodies, in whom lung cancer was detected.