We studied the characteristics of acute blocking of supination of the distal radioulnar joint caused by triangular fibrocartilage complex injuries. Twenty-four patients who were treated for acute blocking of supination were retrospectively assessed. Supination was suddenly blocked after minor trauma to the wrist. Active and passive supination was severely restricted with a mean preoperative range of motion (11°), whereas pronation was almost normal. The cause was identified arthroscopically or at open operation. It was found to be a result of avulsion of the dorsal or palmar portion of the radioulnar ligament, which blocked movement of the ulnar head. Blocking was reduced manually in four cases, by arthroscopic surgery in eight cases and by open surgery in 12 cases. After treatment, forearm supination improved to 84° of the mean range of motion. Distal radioulnar joint blocking from a ruptured triangular fibrocartilage complex should be considered in the differential diagnosis of loss of forearm supination.Level of evidence: IV.