Traumatic epiphyseal dislocation related to birth injury is uncommon. The authors report a case of slipped distal femoral epiphysis during a breech presentation in a twin pregnancy birthing process, diagnosed by ultrasonography. This type of separation could be difficult to detect in the newborn on plain radiographs because of the non-ossification of the epiphysis. Therefore, the use of sonography is helpful to make an early and accurate diagnosis in order to avoid malunion and deformities of the affected limb. Through this case report we will see the diagnostic value of high-resolution ultrasonography in diagnosing newborn injuries of the limbs, and particularly in the diagnosis of radiographically occult epiphyseal separation.