We report three patients (two children and one adult) with Guillain-Barré syndrome and magnetic resonance imaging evidence of gadolinium enhancement of the cauda equina and lumbar nerve roots. All three patients exhibited symmetric ascending paralysis and areflexia, and two (one child, one adult) suffered urinary incontinence and retention. Similar enhancement has been observed in patients with chronic inflammatory demyelinating polyneuropathy and suggests proximal nerve inflammation. Magnetic resonance imaging in Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy may have diagnostic utility.