The posterior reversible encephalopathy syndrome (PRES) is characterized by several neurological signs and symptoms from different pathological causes. The interpretation of magnetic resonance imaging (MRI) is crucial in atypical presentations, to avoid a misdiagnosis and delays in treatment, as in the identification of complicating factors. Differentiating reversible vasogenic edema from cytotoxic edema is possible with diffusion-weighted images (DWI) and apparent diffusion coefficient (ADC) mapping. We present a case of puerperal extensive PRES related to late-onset eclampsia, in a 36-year-old first-time pregnant woman with no previous history of hypertension or other risk factors, associated with a severe clinical picture but with a full recovery in few weeks. We conclude that the prognosis of puerperal PRES should be good, if underlying etiology can be treated satisfactorily, in extensive MRI involvement too.