The authors report a new case of indifference to pain secondary to hereditary sensory neuropathy in a 3 year 9 month-old boy. This child presented with isolated diffuse deficiency of pain and heat sensitiveness with preserved touch without any other neurologic involvement or anhidrosis. Nerve biopsy showed the complete lack of amyelinic fibers. P substance, which might act as a mediator or modulator of the nociception, was absent from the cutaneous nerve endings.