OBJECTIVE AND IMPORTANCE:Arnold Chiari Type I malformation usually presents as headache, arm numbness, dysesthesia, upper weakness, or gait difficulty. We report a case of Chiari malformation presenting as a left trigeminal neuralgia.CLINICAL PRESENTATION:A patient with a history of 29 years of trigeminal neuralgia was admitted. He was treated with three thermocoagulations. Microvascular decompression was planified. Magnetic resonance imaging was performed, and it demonstrated an Arnold Chiari malformation. After surgery, the patient was asymptomatic.INTERVENTION:Posterior fossa decompression by enlarging the foramen magnum and aspiration of the cerebellar tonsils was performed.CONCLUSION:The trigeminal neuralgia could be attributable to a compression of the trigeminal nucleus. The compression of the nucleus could explain both the pain and the regression after surgery. This is the second reported case of pure trigeminal neuralgia in Arnold Chiari malformation.