The origin and histological classification of embryonal tumors, which make up the largest group of malignant pediatric brain malignancies, are two controversial issues. However, in recent years, progress has been made in our understanding of the molecular genetic abnormalities that govern their onset and/or progression. Several of these abnormalities appear to involve alterations in the signaling system controlling normal cerebellar development. An improved understanding of both the biology and clinical relevance of these molecular defects is probably the only means by which neuro-oncologists will improve the management of these tumors, thus reducing disease- and treatment-related morbidity and mortality.