Chemotherapy may be used to delay the need for cranial irradiation in infants and young children with malignant central nervous system (CNS) tumors. The polyfunctional alkylator thiotepa (TT) possesses significant in vitro and in vivo activity in many central nervous system tumors. Before the introduction of a multiagent chemotherapy previously shown to be active in such tumors, thiotepa alone was evaluated in an upfront therapeutic window.