Posterior reversible encephalopathy syndrome (PRES) is a neurotoxic state coupled with a unique radio imaging appearance. We describe this rare, mostly reversible condition in five cases undergoing similar treatment under preset protocol (MCP-841) for acute lymphoblastic leukemia (ALL) at our centre. Hypertension is a well-known adverse effect of high-dose corticosteroid therapy primarily mediated by its effects on the mineralocorticoid receptor especially in pediatric population and we hypothesize that this may be the etiology of PRES in two of these patients.