The present study was performed to describe the morphologic characteristics of the peroneus tertius (PT) tendon, evaluate the variations in its insertion point, investigate the interconnections with the tendons of the extensor digitorum longus, and discuss whether these insertion differences of the muscle tension might have an effect on fracture formation. The length and width of the PT tendon and the width at its midpoint were measured in 44 lower extremities. The data obtained were compared statistically. The PT was found to occur in 2 types according to the number of tendons: type 1, a single tendon without a slip; and type 2, 2 tendons with a slip. It has been suggested that the PT tendon could contribute to avulsion fractures of the tuberosity of the fifth metatarsal bone. Therefore, to understand the mechanism of Jones fracture, knowledge of the PT tendon would be beneficial to determine the insertion points.