Alzheimer’s Disease (AD) is a neurodegenerative disease, characterized by amyloid-ß plaque deposition in the brain, that affects more than 5 million Americans. The glymphatic system is a network of perivascular spaces that facilitates fluid movement and solute clearance from the brain, and its dysfunction in aging has been implicated in the development of AD. The water channel aquaporin-4 (AQP4), located in astrocytic endfeet bordering the perivascular spaces, supports glymphatic function. In the aging rodent and human AD brain, loss of perivascular AQP4 localization is associated with impaired glymphatic function and increased amyloid-ß deposition. Yet the molecular basis for this loss of perivascular AQP4 localization is unknown. Aquaporin-4ex (AQP4ex) is a novel translational readthrough variant of AQP4. Selective deletion of AQP4ex results in the mislocalization of AQP4 all over the astrocytic membrane, indicating that AQP4ex is a crucial element in the perivascular localization of AQP4. In this study, we quantitatively analyze the expression and localization of AQP4ex to determine whether changes in AQP4ex associate with aging, AD status, or AD pathology. Using immunofluorescent double-labeling, confocal microscopy, and custom digital image analysis techniques, we define AQP4ex expression and localization between young and aged mice, and compare these changes between wild-type animals and transgenic animals that spontaneously form amyloid-ß plaques. Using a case series of post mortem human frontal cortical tissue, we compare AQP4ex expression between healthy young adults, cognitively intact aged subjects, and aged subjects with an AD diagnosis. This is the first characterization of AQP4ex expression in the murine brain and in a human case series, and these data will contribute to the small but growing body of research on AQP4ex and its relationship with AQP4 localization, creating opportunities to identify a new novel mechanism and novel target in AD pathology.