We report the case of a 19-year-old patient with an acute-onset non-traumatic coma. Brain MRI scan was normal, CSF showed mild pleocytosis and moderately elevated protein, and continuous EEG-monitoring was compatible with spindle-coma. Cortical somatosensory evoked potentials (SSEPs) and middle-latency auditory evoked potentials (MLAEPs) were bilaterally absent, and brainstem auditory evoked potentials suggested a brainstem dysfunction. Serum anti-GQ1b and anti-GT1a IgG antibodies positivity suggested Bickerstaff's brainstem encephalitis (BBE). The clinical and functional outcomes were favorable and normal cortical SSEPs/MLAEPs reappeared in a few weeks. Based on this report, in cases of unexplained MRI-negative coma with neurophysiological evidence of brainstem dysfunction, BBE should be eliminated before considering withdrawal of life-sustaining therapy (WLST).