Adolescence is a period in which eating disorders and juvenile systemic lupus erythematosus are typically diagnosed. The coexistence of both disorders prompts the search for a common aetiology. In this paper, we present a case of a 16-year-old girl with life-threatening anorexia nervosa followed by clinical and immunological manifestations of systemic lupus erythematosus. The severity of the symptoms of anorexia nervosa resulted in significant delay in proper diagnosis of the concomitant systemic disease which had already been active. The administration of immunosuppressive treatment resulted in decreased lupus activity and resolution of the symptoms of anorexia nervosa.Being affected by one severe and chronic disease does not preclude the coexistence of another disease of different aetiology. However, such coexistence may suggest a common pathophysiology. Many authors have indicated a possible link between anorexia nervosa and many autoimmune disorders. Currently, modern genetic techniques have confirmed a significant correlation between these disorders. This issue needs further investigation and may be helpful in arriving at the final diagnosis in similar cases.