Introduction: Pupillometers objectively measure constriction (i.e., parasympathetic pathway) and dilation (i.e., sympathetic pathway) velocities of the pupillary reflex. These pathways may be affected by increases in ventricular size due to changes in cerebrospinal fluid (CSF) volume, such as during external ventricular device (EVD) weaning in aneurysmal subarachnoid hemorrhage (aSAH) patients. This pilot study evaluated if changes in pupillary responses could be predictive of EVD weaning failure in aSAH patients. Additionally, we analyzed ventricular size and pupillary reactions in these two groups. Methods: Adult aSAH patients serially monitored with the pupillometer at an academic medical center were included. Patients were grouped into those successfully weaned from the EVD and those who were not. Pupillometer measurements (e.g. changes in constriction and dilation velocities), changes in intracranial pressure (ICP), changes in cerebral aqueduct diameter and 3 rd ventricle diameter (measured via computed tomography head (CTH)) were evaluated between the two groups. Results: Seven patients met the inclusion criteria. Three patients required ventriculoperitoneal shunting. There were no significant differences in the changes in constriction or dilation velocities between the groups. Additionally, there was no significant difference in ICP. There were significant differences between the changes in size of the cerebral aqueduct (p=0.01) and of the third ventricle (p=0.01) on CTH between those who weaned and those who did not. These did not correlate with pupillometer measurements. Conclusions: We did not find predictive value in changes in constriction or dilation velocities or ICP on EVD weaning success in aSAH patients. Changes in the diameter of the third ventricle or cerebral aqueduct may be predictive of EVD weaning and suggests a further avenue for study.