Congenital insensitivity to pain with anhidrosis is one of a group of rare diseases termed hereditary sensory-motor neuropathies. Primary clinical features of this entity include congenital analgesia, inability to sweat, and mental retardation. Besides the rarity of these clinical entities, difficulty in evaluating the sensory disturbances, especially in small children, makes the diagnosis a clinical problem. In this article a 3-year-old boy, with consanguineous parents and no family history of the disorder, who was evaluated for two years because of ulcerating lesions on his knees, is presented. Physical examination revealed deep ulceration on his knees and scars from burns on his neck and scalp. Moderate mental retardation and analgesia were noted. There was symmetrical loss of pain and touch sensation on his hands and feet. Electromyographic examination showed absence of action potentials of the ulnar and sural nerves, decrease in the sensory and motor nerve conduction velocities, and amplitude of action potentials. The result of the application of pilocarpine showed anhidrosis. His skin and nerve biopsy specimens were also examined.