An 11-year-old boy with septic arthritis of both knees presented with an anterior mediastinal abscess extending suprasternally. This was drained through a suprasternal incision and the mediastinal cavity was intermittently irrigated with povidone iodine solution and packed with gauze. Staphylococcus aureus was the responsible organism. Antibiotic therapy comprised of cloxacillin and gentamycin. Recovery was uneventful. This is, most probably, the first report on an anterior mediastinal abscess complicating a distant septic arthritis. As for any infective mediastinitis, early diagnosis and aggressive treatment is mandatory for a patient's survival.