Carnotaurus sastrei is a large abelisaurid dinosaur from the Upper Cretaceous of Patagonia. Its remains include an almost complete skeleton with a well-preserved skull and braincase. Because relatively few abelisaurid braincases are known, the description of the Carnotaurus braincase is important for understanding the variability of this complex structure within the clade. Carnotaurus exhibits traits that characterize the abelisaurid basicranium, such as a well-developed preotic pendant, solid basipterygoid processes, and pneumatic basisphenoid, subsellar, and lateral tympanic recesses. The basipterygoid processes do not project laterally, unlike the divergent processes observed in other abelisaurids. Carnotaurus shares with the Malagasy abelisaurid Majungasaurus crenatissimus caudodorsally oriented paroccipital processes and a maxillomandibular foramen for the trigeminal nerve that in lateral view is aligned with the nuchal crest. The detailed description of the braincase of Carnotaurus presented here provides a better cranial anatomical record of this Patagonian abelisaurid and preliminary insights to the neurocranial morphology within the group.