From 1966 to 1981, at "La Paz" Children's Hospital, Madrid, 42 patients with ST were studied. We exclude 4 stillborn, the remaining 38 underwent 40 surgical operations, 69% in the first week of life. The aim of the study is to classify and organize from the clinical and pathological points of view the usual equivocal terminology. From a clinical point of view, sex, localization and age at diagnosis were the usually described for these tumors. The relationship of age with malignancy is pointed out. Special emphasis is made on the pathological information about undifferentiated blastodermic tissues, like neuroblasts pointing out their low influence in prognosis. 79% were mature teratomas and 21% malignant tumors (Yolk sac and embrional carcinoma).