Encephalitis associated with anti-γ-aminobutyric acid-B (GABA B ) receptor antibodies has been identified recently. However, only a few cases have been reported to date and its clinical manifestations and prognosis have not been investigated systematically. We identified five cases of GABA B encephalitis in Korea. Here we present the clinical features, treatment responses, and brain positron emission tomography findings of the cases. The patients had a clinical triad of memory changes, seizure, and association with small-cell lung cancer. Early diagnosis and comprehensive immune modulation may provide a good outcome.