We studied 12 consecutive patients with inflammatory acute transverse myelopathy (ATM) and no prior history of neurologic disease. All had normal pattern shift visual and brainstem auditory evoked potentials. All of nine patients tested also had normal median nerve short-latency somatosensory evoked potentials. None developed new neurologic signs in 18 months' mean follow-up. In contrast, 72% of 50 patients with definite, probable, or possible multiple sclerosis (MS) had abnormalities in at least one evoked potential test. When defined as a virtually or completely transverse inflammatory lesion, acute transverse myelopathy differs from MS.