A 7-year-old female patient with a new diagnosis of ornithine transcarbamylase deficiency was treated for hyperammonemia with a standard protocol. Several days later, she developed ataxia, dysmetria, and dysarthria. Magnetic resonance imaging of the brain demonstrated pontine and extrapontine white matter changes consistent with osmotic demyelination. Classically described as a consequence of hyponatremia treatment, osmotic demyelination syndrome has rarely been associated with other entities. This case suggests a potentially serious complication of the standard therapy for hyperammonemia in patients with ornithine transcarbamylase deficiency.