In studies on family therapy in Anorexia Nervosa, family relationships, as assessed by Expressed Emotion, have been associated with outcome. Our aim was to explore the contribution of Expressed Emotion as a predictor of 18-month outcome, above and beyond the usual predictive factors. Sixty adolescent girls suffering from Anorexia Nervosa and their parents were assessed at baseline and 18 months later. Levels of Expressed Emotion were evaluated in both parents with the Five-Minute Speech Sample. After controlling for treatment group and initial clinical status, high maternal Emotional Over-Involvement at baseline was significantly associated with better clinical state. More precisely, high maternal Emotional Over-Involvement was associated with higher nutritional status, lower eating disorder severity and fewer re-hospitalizations 18 months later. No associations were found with paternal levels of Expressed Emotion. Therefore, our study confirmed the importance of taking into account both maternal and paternal Expressed Emotion. Our results also underlined that high maternal Emotional Over-Involvement plays a positive role in the outcome of Anorexia Nervosa and needs to be explored further.