We present four cases of endodermal sinus tumor affecting children (median age, 20 months). Three tumors were located in the sacrococcygeal region and one in the right testicle. All cases were diagnosed by fine needle aspiration biopsy. The most characteristic features were cells arranged in a papillary-like configuration, vacuolated cytoplasm and intracellular and extracellular deposits of pink, homogeneous material. Immunocytochemical study showed alpha-fetoprotein-positive cells. Ultrastructural study showed intracytoplasmic inclusions of electron-dense material and basement membrane-like material in the intercellular spaces.