Peroneus longus rupture with associated involvement of the os peroneum is an uncommon injury, and a small number of cases have been reported. Several mechanisms of injury have been suggested, but the most accepted theory is due to an inversion force placed on a cavovarus foot type. The sesamoid often becomes the focal point of the mechanical stresses and may fracture. Although the purpose of the sesamoid is to protect the tendon from rupture, the os peroneum may actually encourage fatigue (tear/rupture) under certain circumstances. Because this injury occurs at the cuboid notch, primary repair is complicated because of the inability to access the tendon as it courses deep within the midfoot. We present a bilateral case of peroneus longus rupture with involvement of the os peroneum in a patient with a cavovarus foot type. The injuries were sustained from an identical mechanism and occurred almost 1 year apart. In both situations, a peroneus longus to peroneus brevis tendon transfer was performed above the ankle joint in conjunction with partial excision of the fractured os peroneum. To the authors' knowledge, this is the only reported case of peroneus longus rupture associated with fracture of the os peroneum to occur bilaterally.