It seems clearly evident that the earlier the diagnosis of congenital hypothyroidism is established and adequate therapy is begun the more satisfactory is the prognosis. In a series of 49 cretinous patients seen at the University Hospital the average age at the time of diagnosis was 12 months. We believe that in most of these cases a diagnosis could have been made before 6 months of age. A survey of these patients revealed that 54% had at least three prominent symptoms of their disease by the end of the first month of life and 75%, by the end of the third month. At present there are generally available laboratory studies that can confirm a suspicion of congenital hypothyroidism in better than 90% of cases. Most of the pediatric textbooks and more extensive reference works pay little attention to the early time of appearance of the several important, though nonspecific symptoms