Os vesalianum is a rare accessory bone located proximal to the base of the fifth metatarsal in the peroneus brevis tendon. It is a radiographic diagnosis and mostly an asymptomatic incidental finding with a reported prevalence of 0.1% to 0.9%. Only 11 symptomatic cases have been described in the literature. Surgical therapy has been reported with good outcome in adults, whereas recurrence may follow excision during skeletal growth. We report a case of a 19-year-old girl with chronic weightbearing pain proximal to the base of the fifth metatarsal of her left foot. She first experienced exacerbated pain on increased loading when she started professional training as a shop assistant. Because several months of nonsurgical therapy failed, the decision was made to surgically excise the accessory bone from the peroneus brevis tendon via a longitudinal incision and a simple tendon-to-tendon reconstruction. Postoperative treatment consisted of using a walker to avoid weightbearing for 6 weeks, followed by a gradual return to full weightbearing as tolerated. At final follow-up, the patient was fully asymptomatic and was able to return to work. Citing this case, this article discusses differential diagnoses and treatment options for os vesalianum.