Lipoblastoma, a rare tumor of childhood, was first described by Vellois and associates in 1958. The extremities are the most common location for this tumor. Mediastinal lipoblastoma is exceedingly rare, with only four cases reported in the English-language literature. The authors report a case of mediastinal lipoblastoma in a 6-year-old girl, which, in contrast to previously reported cases, presented late in childhood and included sacrifice of the left innominate vein and phrenic nerve for successful resection.