Congenital insensitivity to pain is a rare clinical syndrome characterized by dramatic impairment of pain perception since birth and is generally caused by a hereditary sensory and autonomic neuropathy with loss of the small-calibre, nociceptive nerve fibres. We report a 9-year-old case, with a generalized congenital insensitivity to pain. The patient was referred to our Department by a private orthodontist for severe limited mouth opening and multiple oral ulcers which greatly worsened after starting the orthodontic treatment. The management of his oral lesions of the limited mouth opening and of the orthodontic treatment are described. The management approach aimed to improve mandibular range of motion and associated stretching and a self-modeling mouthguard to avoid cheek self-biting. This protocol allowed continuing the orthodontic treatment to restore the occlusion. Finally, good occlusion, normal function and better quality of patient's life were achieved.