The pathologic changes in 15 elbows of 14 children (2 bilateral congenital, 12 unilateral posttraumatic, mean age 9.5 years) with radial head dislocation unreduced for at least 3 months (range 3-180 months) and their open treatment were reviewed. Common dysplastic changes observed in both congenital and posttraumatic groups included large deformed radial heads, slender radial necks, and ulnar bowing. Changes were bilateral and symmetrical in the congenital group. In traumatic dislocations, patients with more severe deformities had longer delays from time of injury to time of reduction. Persistent pain, limitation of motion, and deformity were unacceptable symptoms to both patients and their parents, prompting surgical intervention. To produce a smooth rotational arc for the radius and maintain it in stable reduction, restoration of the congruency of the capitello-radioulnar joint and correction of the various dysplastic changes were mandatory during open reduction.