This study aimed to describe the course of early onset eating disorders in a population-based sample followed from 14 to 20 years; identify variables that could account for the persistence of eating disorders from 14 to 20 years; and describe outcome of early onset eating disorders with reference to general and psychological functioning at age 20. Participants (N = 1,383; 49 % male) were drawn from the Western Australian Pregnancy Cohort (Raine) Study, which has followed children from pre-birth to young adulthood. Eating disorder symptoms were assessed using an adapted version of the Eating Disorder Examination-Questionnaire, at ages 14, 17 and 20. At age 14, 70 participants met DSM-IV criteria for a binge eating or purging eating disorder. Nearly half (44 %) of these adolescents ceased to meet criteria for an eating disorders at ages 17 and 20, whilst one-quarter still met criteria for an eating disorder at age 20 and one-fifth met criteria for an eating disorder at all three time points. Purging at age 17 and externalising behaviour problems at age 14 were the strongest predictors of eating disorder persistence to age 20. Participants who experienced a persistent eating disorder were less likely to complete high school than other participants, and reported pronounced depressive and anxiety symptoms at age 20. This study provides new data the course and outcome of early onset eating disorders at a population level. Behavioural difficulties in early adolescence and purging in middle adolescence may predict persistent eating pathology to young adulthood.