Multiple sclerosis (MS) has its usual onset in early adult life (average age of 30 years), but age at clinical onset varies considerably. The implications of the age of onset on the clinical presentation and course of MS are unclear. This population-based retrospective study presents data from a group of 125 patients with onset of MS before age 16 years and can thus be considered as representative of MS occurring in childhood. It demonstrates that childhood MS is more frequent in girls, that it very often has a relapsing-remitting course, that initial bouts usually involve afferent structures of the central nervous system, that recovery from these is often complete, and that the pace of the disease is slow.