Avulsion fractures of the radial wrist extensor from the metacarpal base are rare injuries, and have previously been reported in only a few papers. Although 2 cases of closed rupture of the extensor carpi ulnaris (ECU) were mentioned in 1 report, no case of avulsion fracture of the ECU from its insertion was found in the literature. We recently encountered such a case. The patient, a machine operator, suffered multiple fractures of his forearm, wrist and hand when his left hand was caught in a machine roller. He immediately underwent emergency operation, during which we found the avulsed bone fragment from the ECU insertion. This fragment was retracted to the ECU groove of the ulna, and was located beside the fracture fragment of the ulnar styloid on X-ray. The avulsed fragment was reattached to the base of the fifth metacarpal with Kirschner wires and wire loop, and the patient returned to work 4 months after the operation.