AIM: Assessment of brainstem function plays a key role in predicting the neurological outcome after cardiac arrest. However, the relationship of the two quantitative brainstem assessment methods-automated infrared pupillometry (AIP) and auditory brainstem response (ABR)-with neurological prognoses remains unclear. This study compares the prognostic value of AIP and ABR after cardiopulmonary arrest. METHODS: This retrospective observational study included 124 comatose patients after cardiopulmonary arrest. ABR and AIP measurements were performed simultaneously within 72 h after return of spontaneous circulation. Neurological outcome was assessed at discharge by estimating the cerebral performance category (CPC) score; favourable neurological outcome (CPC score, 1-2) or poor neurological outcome (CPC score, 3-5). The correlation of each AIP parameter and ABR I-V wave latency was tested using Pearson's product moment correlation coefficient, and the prognostic value was compared using the area under the receiver operating characteristics curve (AUC). RESULTS: Pupillary light reflex (PLR) was not detected in 69 patients, and ABR wave V was not detected in 47 patients. All these patients had poor neurological outcome. Among those whose PLR and ABR could be measured, each AIP parameter had a tendency to be correlated with ABR I-V wave latency. Pupil constriction velocity provided the greatest AUC (0.819), with 81% sensitivity and 77% specificity. ABR I-V wave latency provided extremely low AUC (0.560). CONCLUSIONS: Although AIP and ABR were correlated, the AIP measures were superior in predicting the neurological outcome after cardiac arrest as compared with the ABR measures.