We report a rare case of radioulnar dissociation in an 11-year-old boy associated with fracture of the medial humeral epicondyle. Open reduction and Kirschner wire fixation was performed for the epicondylar fracture. The radial head was reduced closed, and the distal radioulnar joint reduced spontaneously. The mechanism of this unusual injury appears to be hyperpronation of the forearm and valgus stress to the elbow.