IN THE past few years a number of cases have been described under the general heading of congenital insensitivity to pain with anhidrosis. In the present article an additional case is reported and a defect in neural crest differentiation proposed as the common underlying embryonic abnormality. The syndrome consists of the following: (1) loss of deep and/or superficial pain sensibility; (2) autonomic dysfunction manifested by (a) pupillary abnormalities ranging from a partial to complete bilateral Horner's syndrome, (b) neurogenic anhidrosis with otherwise normal sweat glands, (c) vasomotor instability with abnormal vanillylmandelic and homovanillic acid urine assays; (3) aplasia of dental enamel; (4) meningeal thickening and cystic change; (5) mild mental retardation; (6) hyporeflexia; (7) blond hair, blue or blue-green eyes, and fair complexion. Report of a Case A five-year-old, white boy of Scandinavian extraction was first hospitalized at Childrens Hospital, Los Angeles, on Aug 10, 1965, with a presenting complaint