We report a case of reversible posterior leukoencephalopathy syndrome in a 50-year-old patient with severe untreated hypertension. Recent advances in magnetic resonance imaging (especially diffusion-weighted imaging) allow new pathopysiological insight: it was found that the resulting vasogenic edema was restricted neither to the posterior vascular territories nor to white matter. The apparent diffusion coefficient helps to differentiate between reversible vasogenic edema and cytotoxic edema, the latter indicating irreversible neuronal death.