Lesch–Nyhan syndrome (LNS) is an X-linked recessive disorder resulting from a deficiency of the metabolic enzyme hypozanthine–guanine phosphoribosyltransferase (HPRT). This syndrome presents with abnormal metabolic and neurological manifestations including hyperuricemia, mental retardation, spastic cerebral palsy (CP), dystonia, and self-mutilation. The mechanism behind the severe self-mutilating behavior exhibited by patients with LNS is unknown and remains one of the greatest obstacles in providing care to these patients. This report describes a 10-year-old male child with confirmed LNS who was treated for self-mutilation of his hands, tongue, and lips with repeated botulinum toxin A (BTX-A) injections into the bilateral masseters. Our findings suggest that treatment with BTX-A affects both the central and peripheral nervous systems, resulting in reduced self-abusive behavior in this patient.