Lipoblastoma is a rare, benign, fatty tissue tumor that occurs in childhood. The location of this tumor in the mediastinum and extension to the chest wall is uncommon. We describe a 12-month-old male infant with a mediastinal lipoblastoma discovered because of a chest wall swelling. Computed tomography showed the deep component and fatty content of the lesion suggestive of the diagnosis. Total excision of the mass was carried out. The histologic examination of the lesion confirmed the diagnosis of lipoblastoma.