A fracture of the os peroneum is a rare cause of ankle and foot pain and is often overlooked and not assumed. Only a few case reports have discussed the different etiologies, options for diagnosis, and therapeutic interventions for acute cases. We present a case of delayed diagnosis of an os peroneum fracture due to a distortion of the ankle that occurred during air sports. Initial diagnostic testing with magnetic resonance imaging demonstrated a rupture of the peroneus longus tendon with no pathologic abnormalities at the peroneus brevis tendon. During surgery, a combination of an os peroneum fracture and a peroneus brevis tendon split was found and was successfully treated with bone and tendon repair using a lasso stich technique.