A case of infiltrating lipoma of the buttock in a 21-month-old child is reported. The tumor, measuring 9 x 12 cm, was situated between the gluteal muscles with a lobulation penetrating into the pelvis through the obturator foramen. It was adherent to, but not infiltrating the sciatic nerve. Few cases of infiltrating lipomas in pediatric patients have been reported in the literature. The diagnosis is based mainly on clinical examination and CT. Fine-needle aspiration may be useful preoperatively to exclude a liposarcoma. Recurrences are frequent when follow-up is adequately extended. For optimal therapeutic results the excision of the tumor should include a rim of adjacent muscle tissue.