Acute intermittent porphyria (AIP), an autosomal dominant disorder, results from a deficiency of the enzyme hydroxymethylbilane synthase. Despite important advances in the characterization of AIP, the pathophysiology of the neurologic manifestations is not clearly understood. We present a patient with AIP followed for 31 years with multiple episodes of hyponatremia during AIP exacerbations. We discuss the clinicopathologic correlation and possible explanations for the morphologic findings, including discrete hypothalamic changes.