We report a 13-month-old boy with diencephalic syndrome (DS) due to an optico-hypothalamic juvenile pilocytic astrocytoma (JPA). Massive neuroaxis dissemination was identified at diagnosis. He received 6 courses of combined conventional-dose chemotherapy consisting of carboplatin (CBDCA), etoposide (VP-16), and cyclophosphamide (CPA) followed by high-dose chemotherapy with CBDCA, CPA, and ranimustine (MCNU) and peripheral blood stem cell transplantation (PBSCT). This treatment produced tumor regression in both intracranial and spinal lesions and remarkable improvement of DS. The rare combination of DS and symptomatic neuroaxis dissemination of JPA at diagnosis suggests that the behavior of some of these tumors is more aggressive and resistant to conventional-dose chemotherapy than is that of JPA without DS manifestation and dissemination.