We describe the radiographic findings associated with occult upper tibial fractures in infants and young children and offer an explanation for the underlying mechanism from which they result. These fractures tend to be subtle, just as the classic spiral tibial fracture originally described by Dunbar et al. (1964, J Can Assoc Radiol 15: 136-144). The fracture we describe results from a hyperextension injury to the knee, and the knowledge of the mechanism of injury, the subtle radiographic findings, and the findings on physical examination allow one to diagnose this fracture with confidence. Otherwise, it easily can go undetected.