Tehran University of Medical Sciences Journal of Orthopedic and Spine Trauma 2538-2330 8 4 2022 12 04 148 150 Mahmoud Farzan Department of Orthopedics, Imam Hospital Complex, Joint Reconstruction Research Center, Tehran University of Medical Sciences, Tehran Iran. Abbas Abdoli Department of Orthopedics, Shahid Sadoughi Hospital, Shahid Sadoughi University of Medical Sciences, Yazd, Iran Mohammad Sadeghian Joint Reconstruction Research Center, Tehran University of Medical Sciences, Tehran Iran Mitra Ashrafi Joint Reconstruction Research Center, Tehran University of Medical Sciences, Tehran Iran Mahsa Akhtarzadeh Joint Reconstruction Research Center, Tehran University of Medical Sciences, Tehran Iran Shahram Akrami Joint Reconstruction Research Center, Tehran University of Medical Sciences, Tehran, Iran Amir Reza Farhoud Department of Orthopedics, School of Medicine, Joint Reconstruction Research Center, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran 2022 04 02 2022 05 10 Background: Entrapment of the ulnar nerve in the cubital tunnel occurs as the second most common compression neuropathy of the upper limb. Although the usual etiology is idiopathic or following cubitus valgus, a compressing mass can be a rare ca use and should be considered in atypical presentation. Case Report: A 45-year-old male patient presented with subacute onset of cubital tunnel syndrome that progressed rapidly and was associated with significant pain. An intra-canal ganglion cyst was found during surgical decompression of the ulnar nerve. Conclusion: Diagnosis of intra-cubital canal mass should be considered when sudden onset and rapid progression of the cubital tunnel syndrome and dramatic pain coincide. Imaging modalities like ultrasound or magnetic resonance imaging (MRI) may be helpful to reach the correct diagnosis before the surgery.   https://jost.tums.ac.ir/index.php/jost/article/view/383 https://jost.tums.ac.ir/index.php/jost/article/download/383/293