Hemolymphoproliferative diseases and brain tumors are among the most common causes of morbidity and mortality in children. In the past few years, increased effectiveness of treatment modalities has significantly increased overall survival, but has also disclosed new aspects of the natural history of these disorders, among which central nervous system involvement due to iatrogenic side-effects. Magnetic resonance imaging plays an important, often crucial, role in the diagnosis of several of these disorders. Close interdisciplinary collaboration between hemato-oncologists and neuroradiologists is of paramount importance to provide affected children with an early diagnosis and proper treatment.