We describe an adolescent girl with non-paraneoplastic anti-NMDA-receptor encephalitis (ANMDARE), who despite persistence of the extreme delta brush (EDB) pattern for nearly 2 years in her serial EEGs, she exhibited a speedy and sustained response to immunotherapy. To the best of our knowledge, our patient had the longest persistence of the EDB pattern on EEG reported to date. Our patient illustrates that, although presence of EDB supports the diagnosis of ANMDARE, its presence and persistence may not be a reliable predictor of response to immunotherapy and overall clinical prognosis.