Avascular necrosis after fracture of the talus is well recognized, but is very rare in children. We report a case of avascular necrosis of the talus simulating juvenile idiopathic arthritis. The diagnosis was confirmed by open biopsy, and non-operative treatment was performed. The patient was asymptomatic with full range of motion postoperatively for two years. We hypothesize that avascular necrosis of the talus without fracture and dislocation might be caused by soft tissue damage around the talus with repeated hyperflexion of the ankle joint and slow arterial occlusion.