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Dougho Park,1 Byung Hee Kim,1 Sang-Eok Lee,1 Dong Young Kim,2 Yoon Sik Eom,2 Jae Man Cho,3 Joong Won Yang,3 Mansu Kim,3 Heum Dai Kwon3 1Department of Rehabilitation Medicine, Spine and Joint Center, Pohang Stroke and Spine Hospital, Pohang, Republic of Korea; 2Department of Orthopedic Surgery, Spine and Joint Center, Pohang Stroke and Spine Hospital, Pohang, Republic of Korea; 3Department of Neurosurgery, Spine and Joint Center, Pohang Stroke and Spine Hospital, Pohang, Republic of KoreaCorrespondence: Dougho ParkDepartment of Rehabilitation Medicine, Spine and Joint Center, Pohang Stroke and Spine Hospital, 352, Huimang-Daero, Nam-Gu, Pohang, 37659, Republic of KoreaTel +82 54 289 9171Fax +82 54 289 9100Email parkdougho@gmail.comPurpose: A bifid median nerve (BMN) is not a rare variant. This study aimed to investigate the features of carpal tunnel syndrome (CTS) accompanied by BMN.Patients and Methods: In this retrospective study, we defined a BMN group as CTS with BMN and a non-bifid median nerve (NMN) group as CTS without BMN. All hands were assigned to four severity grades according to the findings of electrodiagnosis (EDx): very mild, mild, moderate, and severe. The cross-sectional area (CSA) of the median nerve, palmar bowing of the flexor retinaculum, and persistent median artery (PMA) were assessed by ultrasonography. Numerical pain rating scale (NRS) and symptom duration were assessed as clinical variables.Results: Sixty-four hands (57 patients) and 442 hands (341 patients) were enrolled in the BMN and the NMN groups, respectively. BMN was prevalent in 12.6% of all CTS hands. The distribution of EDx severity grade was milder in the BMN group than in the NMN group (P< 0.001). The CSA of the BMN group was 16.2± 4.1 mm2, slightly larger than 15.1± 4.2 mm2 in the NMN group (P=0.056). The BMN group showed higher NRS than the NMN group (5.5± 1.5 and 4.4± 1.7, respectively; P< 0.001). In the subgroup analys