Acute hyperammonemia is a medical emergency requiring rapid recognition and treatment to prevent devastating neurologic sequelae. Its varying etiologies include primary hepatic failure, drug toxicity, infection, and inherited disorders of metabolism. Ornithine transcarbamylase (OTC) deficiency is the most common inherited urea cycle disorder and can result in hyperammonemic encephalopathy and coma, often presenting in the newborn or early childhood. Partial deficiencies of the enzyme can present later in adulthood with protean neuropsychiatric signs and symptoms. Early recognition and management of metabolic encephalopathy is crucial to avoid neurologic damage, and may require hemodialysis for rapid removal of ammonia, with adjunctive medications and dietary modifications to decrease endogenous nitrogen production and activate alternate pathways of nitrogen excretion. We present the case of an adult patient with partial OTC deficiency who presented with encephalopathy, coma, and seizures, accompanied by hyperammonemia and treated acutely with hemodialysis.