I studied the anatomical relationships in thirty-two transitional fractures of the distal part of the tibia by standard radiography and in thirteen of these patients by computerized axial tomography. Three different configurations of fractures could be identified: biplane fractures and two different types of triplane fractures (Type I and Type II). In the biplane lesion the fracture is restricted to the epiphysis, while the triplane fractures are characterized by a wedge of metaphyseal bone. In the Type-I triplane lesion the metaphyseal portion of the fracture ends in the physis, while in the Type-II triplane lesion the metaphyseal portion of the fracture line extends through the physis into the epiphysis and the joint. On the anteroposterior radiograph, the epiphyseal fracture line in both the biplane and the two types of triplane fractures may be found anywhere from the extreme medial to the extreme lateral position. Its location, however, is exclusively dependent on the maturity of the distal tibial physis and is not influenced by the mechanism of injury. The use of computerized axial tomography has revealed the true dimensions of these fractures, and the diagnosis of biplane and triplane fractures can now be made by standard radiography alone. However, the evaluation of undisplaced or only slightly displaced Type-II triplane fractures will still occasionally require the use of computerized axial tomography. Displaced transitional fractures with a fracture gap of more than two millimeters in the weight-bearing portion of the epiphysis require open reduction. If the gap is less than two millimeters, non-operative treatment with a plaster cast is sufficient.