A young child with neurofibromatosis type 1 (NF1) is reported who developed two primary malignancies: a glioblastoma, followed 6 months later by an abdominal B cell non-Hodgkin's lymphoma. The child is now 4.5 years off treatment and disease free, but has developed progressive and severe psychomotor retardation as sequelae. The NF1 gene is known to act as a tumor suppressor gene. The possible mechanisms leading to the occurrence of a second primary tumor in this child are discussed.