Nail biting is a phenomenon which is frequently observed and often accepted by society. The word onychophagia comes from the Greek onycho meaning nail and phagos meaning to eat. Onychophagia is a disorder that consists of habitual, repetitive nail biting together with their swallowing. In onychotillomania the nail plate is destroyed by mechanical damage. Both disorders are classified in the obsessive-compulsive spectrum. Onychophagia is most frequently observed in teenagers, who constitute about 45% of all cases. The aetiology of habitual nail biting is extremely difficult to establish. The cause of onychophagia may be stress, anxiety, loneliness and passivity. The consequences of onychophagia and onychotillomania are problems affecting the nail apparatus, the whole stomatognathic system and, in rare cases, systemic infections. It is postulated that treatment should consist of both pharmaco-therapeutic elements and behavioural therapy.