The use of empirically supported treatment (EST) has been shown to enhance treatment outcome. The purpose of this case study was to suggest that ESTs further encourage effective reconceptualisation and the ongoing delivery of effective treatment, especially in the case of complex or atypical presentations or response to treatment. This report describes the case of an adolescent girl who underwent Maudsley family-based treatment for anorexia nervosa (AN) for a period of 12 months. Atypical response lead to an understanding of her presentation as representing a primary conversion disorder, within which AN symptoms were conceptualised as another somatic conversion of emotional distress. The report details her clinical presentation and management over the course of her illness. The case offers an important opportunity to explore the central role of the use of ESTs in guiding effective treatment delivery.