Maladaptive body size evaluation processes and body dissatisfaction are known as central risk factors for the development and maintenance of anorexia nervosa (AN). This study aimed to experimentally test potential key facets, such as (psycho)physiological, cognitive-verbal and behavioral mechanisms, within the context of these evaluation processes. Twenty-two females with AN (AN-G) and 22 healthy controls (HC-G) looked at pictures of their body gradually increasing in weight using a morphing technique. Implicit emotional arousal was assessed using steady-state visual evoked potentials (SSVEP) in electroencephalography. Additionally, in a forced-choice body size evaluation task, participants were asked to classify pictures of their own body as not big or big while reaction times were captured. A significantly earlier increase in SSVEPs emerged in AN-G compared to HC-G (p <.05), with AN-G evaluating their bodies in the morphing process as big at a significantly thinner body size (p <.05). The AN-G showed faster reaction times in the categorical evaluation of body stimuli (p <.05). Findings from this multimodal paradigm underline the importance of body size evaluation mechanisms and underlying emotional arousal for AN. A differentiated understanding of these processes is essential, since the effectiveness of therapeutic interventions for AN is limited and relapses are frequent.