A 13-mo-old intact male African lion (Panthera leo) presented with a 3-mo history of lethargy, ventral flexion of the neck, abnormal vocalization, and ataxia. Hemogram and serum biochemistries were within normal limits except for the presence of hypokalemia (2.7 mEq/L) and hypochloridemia (108 mEq/L). When no improvement was noted with oral potassium gluconate supplementation, a computed tomography scan of the brain and skull was performed, and no abnormalities were noted. However, magnetic resonance imaging detected occipital bone thickening, crowding of the caudal cranial fossa with cerebellar compression and herniation, and cervical syringohydromyelia, which was consistent with a Chiari I–like malformation. Foramen magnum decompression was performed to relieve the compression of the cerebellum. The animal recovered well with subsequent resolution of clinical signs. Hypovitaminosis A has been proposed previously as the underlying etiology for this malformation in lions with similar clinical presentations. This lion's serum and liver vitamin A concentrations were low (100 ng/ml and 25.31 μg/g, respectively) compared to concentrations reported for domestic carnivores and support hypovitaminosis A as the underlying cause of this animal's Chiari I–like malformation.