Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is a treatable but often misdiagnosed autoimmune encephalitis. Diagnosis depends on NMDAR antibody testing, which may not be readily available. Alternatively, the electroencephalogram (EEG) extreme delta brush pattern may provide a valuable immediate indicator for the diagnosis of anti-NMDAR encephalitis. A 32-year-old female (case 1) presented with fever, headache, behavioral changes, confusion, intractable seizures, central hypoventilation, dysautonomia, facial and limb dyskinesias, and comorbid ovarian teratoma. Cerebral spinal fluid (CSF) testing revealed mild lymphocytic pleocytosis while brain MRI results were normal. A 45-year-old male (case 2) presented with major behavioral changes and rare seizures. Results of routine CSF testing and brain MRI scanning were unremarkable. In both cases, EEG initially revealed the extreme delta brush (EDB) pattern of beta bursting on the peaks and/or the troughs of delta waves, which led to subsequent NMDAR antibody testing and the confirmative diagnosis. Thus, EDB may be a readily accessible sign for suspected anti-NMDAR encephalitis.