A 15-year-old boy without any medical history was referred to our hospital for osteomyelitis of the sternum and a subcutaneous abscess extending over half of the anterior chest wall. The patient's chest had been elbowed by an opponent during a basketball game 19 days earlier. He stated that there were no abrasions or lacerations at the time of injury, but 10 days later, he developed chest wall swelling (Figure 1) and fever. He consulted a local orthopedist and underwent chest computed tomography (CT), leading to provisional diagnosis. The chest mass was punctured, and the pus was drained. Subsequently, the patient was sent to our hospital. Chest CT revealed a sternal fracture and extensive fluid collection in the chest wall (Figure 2(a)). Increased density of the region behind the sternum was also observed, but we concluded that inflammation had not affected the anterior mediastinum. Because the patient did not appear severely ill, we performed pus drainage from a minimal incision and subcutaneously applied a 19 Fr silicone drain connected to a closed drainage system (BLAKE drain and J-VAC Reservoir; Johnson and Johnson Medical, Tokyo) under general anesthesia. The drained material yielded a Staphylococcus aureus isolate on microbiological culture; this culture was sensitive to all antibiotics tested. The patient was treated by intravenous administration of sulbacillin for 2 weeks, followed by oral administration of tosufloxacin for 10 days. The drain was removed on postoperative day 14. The patient was discharged on postoperative day 26, and antibiotic therapy was discontinued. While infectious granulation was observed at the drain tube-penetrating site for a few months after discharge, complete epithelialization of the site was confirmed 4 months after the surgery. Follow-up CT performed 4 months after surgery showed disappearance of fluid collection and ossification of the fracture site (Figure 2(b)). The patient did not show any symptoms and signs of recurrence 6 months after the surgery.