Posterior internuclear ophthalmoplegia is a rare sign of pons infarction.Due to its mild clinical symptoms,it is easily misdiagnosed.In this article,we report a case of posterior internuclear ophthalmoplegia caused by pons infarction,discuss the causes of misdiagnosis and hope to attract the attention of doctors.By analyzing the clinical features of the case and reviewing the literatures,we try to differentiate the disease from multiple sclerosis,pons tumors and other diseases.The diagnosis was confirmed with thorough physical examination,laboratory test and imaging examination.Posterior internuclear ophthalmoplegia is a sign of pons infarction.