A 4½-week-old boy had acute onset of respiratory distress and anemia. A chest roentgenogram demonstrated a large anterior mediastinal mass. Laboratory studies and clinical course were consistent with nonconsumptive coagulopathy and acute blood loss. The coagulopathy was responsive to fresh frozen plasma and vitamin-K therapy. Thoracotomy disclosed an enlarged, hemorrhagic thymus, which was excised. This entirely relieved the respiratory distress. Microscopical examination showed hemorrhage into an otherwise normal thymus, a previously unreported phenomenon, to the authors' knowledge. The possible cause of the hemorrhage was late-onset hemorrhagic disease of the newborn.