Topiramate has recently been reported to cause hyperthermia as a result of oligohydrosis, primarily in pediatric patients. All cases reported to date were clinically mild, without permanent systemic or neurologic dysfunction. We report a case of severe hyperthermia and subsequent ataxia and tremor in an adult treated with topiramate. To our knowledge, this is the first case of topiramate-associated hyperthermia to result in residual cerebellar and cognitive dysfunction.