Intellectual disability is a deficit in intellectual functioning that impairs adaptation to daily life and may lead to behavioural disorders. Self-injury behaviour is a form of behavioural disorder which has an association with intellectual disabilities in children. Self-injury behaviour can be present in certain genetic syndromes, such as Lesch–Nyhan syndrome. A two-year-old boy with developmental delay was unable to sit, crawl, and talk. He had a habit of biting his lips, tongue, and fingers frequently. His uric acid level was 7.3 mg/dL. The patient was diagnosed with behavioural and emotional disorder with global developmental delay due to suspected Lesch–Nyhan syndrome. In this case, self-mutilating behaviour, global developmental delay, and motor impairment were observed. Integrated management through behavioural therapy and combination pharmacologic interventions represents the current therapeutic approach. Self-mutilating behaviour accompanied by motor impairment may give rise to physical deformity and decrease a child’s quality of life if not diagnosed and treated early.