A case of traumatic posterior dislocation of the hip in a child in which the diagnosis was initially missed is presented. The fact that the condition may follow extremely mild trauma is demonstrated, and the need for two-plane radiography is stressed. A review of the literature emphasizes that prompt recognition and treatment may markedly reduce the incidence of avascular necrosis of the femoral head, the commonest and most severe complication. Reduction of a traumatically dislocated hip in a child is usually easy and need not be performed only at specialist centres.