Fracture of os peroneum can occur, but the fracture fragments are seldom displaced. Complete rupture of peroneus longus through the fracture of the os peroneum causing displacement of the fracture fragments is not well reported in the literature. Differential diagnosis with bipartite os peroneum or calcific tendinitis is important because misdiagnosis of the tendon rupture can lead to serious sequela including chronic pain, ankle instability, and peroneal compartment syndrome. We report a case of complete rupture of peroneus longus associated with fracture of the os peroneum with a review of the literature.