INTRODUCTION: Immune effector cell-associated neurotoxicity syndrome (ICANS) is a common side-effect of chimeric antigen receptor T-cell (CAR-T) therapy, with symptoms ranging from mild to occasionally life-threatening. The neurological, cognitive, psychiatric and psychosocial sequelae of ICANS are diverse and not well defined, posing a challenge for diagnosis and management. The recovery trajectory of the syndrome is uncertain. Patients are rarely examined in this population pretherapy, adding a layer of complexity to specifying symptoms pertinent solely to CAR-T treatment. We present a protocol of a prospective longitudinal research study of adult patients in a single Australian haematology service undergoing CAR-T therapy. The study will describe neurocognitive features specific to ICANS, characterise the underlying syndrome, capture recovery, identify predictors of differential postinfusion outcomes and determine a set of cognitive instruments necessary to monitor patients acutely. METHODS AND ANALYSIS: This is a prospective longitudinal study that comprises neuropsychological and neurological examinations occurring prior to CAR-T, during the acute post-treatment period, 28 days, 6 months and 12 months post infusion. Data will be sourced from objective psychometric measures, clinical examinations, self-report questionnaires of psychopathology and accounts of subjective cognitive complaint. ETHICS AND DISSEMINATION: This study aims to guide diagnosis, management and monitoring of neurocognitive features of CAR-T cell therapy. Results of this study will be disseminated through publication in peer-reviewed journals and presentations at scientific conferences. All procedures involving human subjects/patients were approved by the Peter MacCallum Cancer Centre Human Research Ethics Committee (21/145).