The authors offer three interpretations of onychophagia, a widespread but largely unstudied phenomenon. The first is phenomenological, and characterises onychophagia as a non-pathological behavioural symptom present in many pathologies and a distinct syndrome that is sometimes quite severe. The second is clinical, and indicates the convergent and divergent connections between onychophagia and the most frequent eating disorders. The third is psychodynamic, and suggests an interpretative hypothesis of onychophagia itself and the frequent sensation of trouble and refusal that it often provokes even in doctors and psychotherapists.