Background: Compulsive exercise (CE) has been proposed as significant in the etiology, development and maintenance of eating disorders (EDs), resulting in more severe and enduring pathology. However, few studies have investigated CE longitudinally in adolescents with EDs. We aimed to test if adolescents show the same associations between CE and other clinical variables as previous research has found in adults. Methods: Three thousand one hundred sixteen girls and 139 boys from a clinical ED database were investigated regarding prevalence and frequency of CE and its relation to psychiatric symptoms, associated features and outcome. Denial of illness is common among adolescents and was therefore adjusted for. Results: Adjusted CE prevalence in girls was 44%, and CE was most prevalent in bulimia nervosa. As previously found in adults, those with CE scored significantly higher than non-CE on total ED severity, level of restriction and negative perfectionism. However, there were only minor differences between CE and non-CE patients on emotional distress, hyperactivity, suicidality and self-esteem. Among boys, adjusted CE prevalence was 38%, and CE boys scored significantly higher than non-CE on total ED severity. Initial CE did not influence 1-year outcome, although cessation of CE was associated with remission. Conclusions: CE is a common clinical feature in adolescents with EDs and cessation is associated with remission. When controlling for denial of illness, CE had less detrimental impact than predicted. We recommend controlling for denial in studies on ED adolescents and further exploration of classification and treatment implications of CE.