We report two patients with acute hyponatremic encephalopathy which developed after massive water ingestion for pelvic ultrasound and emphasize the findings of magnetic resonance (MR) imaging including diffusion-weighted imaging (DWI). Both subjects had completely recovered within 24 hours following fluid restriction and salt replacement. MR imaging revealed cortical sulcal narrowing, restricted diffusion and sulcal T2 hyperintensity along with diffuse pial enhancement suggesting diffuse cerebral cortical cytotoxic edema and blood-brain barrier breakdown. In addition to the first illustration of multimodality MR imaging features of water-intoxication, these two cases also highlight the need for standardized practice on the quantity of water intake recommended to distend the bladder for pelvic ultrasound, especially in patients at risk for serum inappropriate ADH syndrome-related hyponatremia.