BACKGROUND Acute blockage of forearm supination has been reported in several studies. It is caused by loose bodies in the wrist joint, extensor carpi ulnaris tendon interposition, and distal radioulnar joint (DRUJ) injuries, including forearm bone fractures. Some studies have reported cases of DRUJ injuries caused by triangular fibrocartilage complex (TFCC) tears.We report a case of acute blockage of forearm supination after minor trauma and suggest a possible TFCC tear when a patient complains of forearm supination blocking. In addition, we present a comparison between our case and other reports on etiology, magnetic resonance imaging (MRI) findings, and arthroscopic findings, and show the specific characteristics of our case. METHODS A 22-year-old male presented with left wrist pain as the chief complaint. He was injured 2 months prior to pushing his left hand on the floor during exercise. Physical examination showed a relative limitation of range of motion (ROM) in the left wrist of about 10° in flexion and about 15° in extension compared with the right side. The patient also complained of supination limitation and volar side wrist pain during supination. The patient showed tenderness in the axial compression test. METHODS Plain radiographs showing no abnormalities. MRI showed a TFCC tear in the central portion. A torn flap of the TFCC was interposed on the volar side of the DRUJ. METHODS Arthroscopic surgery of the left wrist joint was performed. Arthroscopic examination revealed a tear in the TFCC on the radial side. A torn flap was interposed on the volar side of the DRUJ. We removed the flap from the DRUJ using an arthroscopic grasper and partially resected it. RESULTS Intraoperative tests showed no locking and the forearm was well supinated. Two months after the surgery, the patient had no pain and showed full forearm supination. CONCLUSIONS DRUJ blocking due to a TFCC tear should be suspected when acute blockage of forearm supination occurs after minor trauma. MRI is helpful for diagnosis; however, we suggest that the diagnosis should be confirmed through arthroscopy. Symptoms can be resolved by surgical treatment using arthroscopy.