A diagnostic process in a 13 year-old boy with a parainfectious transverse myelitis is described. Its onset was acute, with L1-location level of lesion. After a mild improvement, a relapse happened 26 days later, with a D6 level and without subsequent recovery. It has not been found criteria for diagnosis of multiple sclerosis, nor data suggesting a vascular or ischaemic anomaly. Likewise, other causes and specific infections were rejected, being cataloguet as parainfectious etiology, due a previous viral infection before its onset.