N-methyl-D-aspartate receptor (NMDAR)-antibody encephalitis is a life-threatening neuropsychiatric disorder requiring prompt immunotherapy. The earliest features are mental-state changes, often mistaken for primary psychosis. Improved clinical differentiation could assist rational diagnostic investigation and expedite immunotherapy. Inspired by patients’ and relatives’ lived experience, we aimed to explore the psychiatric phenotype of NMDAR-antibody encephalitis and the features common to and distinct from real-world episodes of psychosis.