A discoid medial meniscus is a relatively rare pathology of the knee joint, and we recently encountered a patient with discoid medial meniscus, and this report is a case of therapeutic experience in this patient. The patient was twenty years old man who had a persistent dull pain for several years without specific trauma history. He was presumptively diagnosed as discoid medial meniscus by MRI, and arthroscopic examination confirmed the presence of the complete type of discoid medial meniscus with horizontal tear. We performed arthroscopic partial meniscectomy, and the patient could get free from symptom.