Self-illness ambiguity is a difficulty to distinguish the ‘self’ or ‘who one is’ from one's mental disorder or diagnosis. Although self-illness ambiguity in a psychiatric context is often deemed to be a negative phenomenon, it may occasionally have a positive role too. This paper investigates whether and in what sense self-illness ambiguity could have a positive role in the process of recovery and self-development in some psychiatric contexts by focusing on a specific case of mental disorder – anorexia nervosa.