Posterior reversible leukoencephalopathy syndrome (PRES) is a clinical radiographic syndrome of heterogeneous etiologies characterised by acute neurological symptoms of brain dysfunction with MRI abnormalities, primarily in posterior cerebral white and grey matter. In most cases, symptoms resolve without neurological consequences. The paper reports the case of a 13-year-old teenager who showed hypertension and altered consciousness with status epilepticus at the electroencephalographic (EEG) monitoring three days after Acute Lymphoblastic Leukaemia diagnosis. The only therapy she went through was prednisone. At the diagnosis of PRES hypertension is frequent but not invariable. The hypertensive crisis may precede the neurologic syndrome by 24 hours or longer. In the paediatric population seizures and/or status epilepticus are often the presenting manifestation. Neuroimaging is essential to the diagnosis of PRES; typical findings are bilateral areas of white matter oedema in the posterior cerebral hemispheres, particularly the parieto-occipital regions, but variations do occur. Treatment is a symptomatic and supportive therapy. In many cases, PRES seems to be fully reversible within a period from days to weeks, after removal of the inciting factor and control of the blood pressure. Radiologic improvement is slower than clinical recovery.