Lipoblastoma is a rare benign tumor arising from embryonic fat; it occurs mainly in the extremities and almost exclusively in infants and children younger than 3 years. We present a case of giant mediastinal lipoblastoma in a 16-month-old boy who presented with acute respiratory distress. The mass was completely excised through a left posterolateral thoracotomy. The postoperative course was uneventful, and the pathologic final diagnosis was lipoblastoma. Although extremely rare, mediastinal lipoblastoma can be life threatening; therefore, it should be included in the differential diagnosis of mediastinal mass in younger subjects.