Acute disseminated encephalomyelitis (ADEM) is an uncommon disease characterized by inflammation and demyelination of the central nervous system (CNS). It typically occurs after a viral infection or vaccination and is more frequent in children. Its immediate and longterm prognosis is expected to be good (20% of cases with sequelae). Although ADEM is typically monophasic, occasional relapses may occur. Differential diagnosis, mostly in the early phases, is established with multiple sclerosis (MS), a chronic inflammatory demyelinating disease of the CNS that may have worse prognosis. Traditionally it has been believed that 10% of ADEM patients develop MS. However, this percentage could be higher according to several recently published clinical series. Some clinical and paraclinical patterns are considered to confer risk of developing MS when present in ADEM patients. Our study has aimed to: a) describe a series of 29 patients (22 children and 9 adults) admitted in our hospital and diagnosed of ADEM between 1990 and 2005; b) study those patients considered to have risk patterns of developing MS, and c) compare the child and adult populations of our series. After a median 55 month follow-up, 6 children (27%) and no adults developed MS. In our series, risk patterns for developing MS predicted conversion to MS more accurately in children than in adults. Eight patients (6 children and 2 adults) had sequelae, cognitive in 6 of them. Our work supports that also observed in recent publications: that both conversion to MS or presence of sequelae after an episode of ADEM are more frequent than traditionally considered.