Autoimmune encephalitis are brain inflammatory processes that are classified into two main groups according to the underlying pathogenic mechanism: antibodies to intracellular antigens (paraneoplastic) and antibodies to extracellular or neuronal surface antigens. The clinical manifestations of autoimmune encephalitis are very varied and non-specific. Complementary tests included in its clinical diagnosis include determination of antibodies in serum or cerebrospinal fluid and magnetic resonance imaging (MRI). MRI may show characteristic patterns such as mesial temporal involvement, although in some cases it may be normal or non-specific. 18F-Fluorodeoxyglucose PET/CT (18F-FDG PET/CT) imaging may be helpful in cases of paraneoplastic autoimmune encephalitis to find the primary tumor. In autoimmune encephalitis mediated by antibodies to extracellular antigens, 18F-FDG PET/CT shows distinctive patterns that can aid clinical diagnosis. This continuing education aims to present in a clear and easy-to-understand way, the clinical features of autoimmune encephalitis, the difficulties in clinical diagnosis and the patterns seen on MRI and 18F-FDG PET/CT.