The clinical manifestations of biochemically-confirmed acquired hypothyroidism in nineteen children and adolescents were reviewed to evaluate the symptoms and signs in the early stage of the disease. The group consisted of 14 girls and 5 boys ranging in age from 4 to 15 years. In 13 of the 19 patients with profound biochemical hypothyroidism, classical symptoms were often absent and clinical signs limited. In these patients, hypothyroidism was presumed to have been short in duration and consequence of chronic lymphocytic thyroiditis. In the remaining 6 patients, hypothyroidism was long-standing and clinical presentation classical, including disproportionate weight gain, fatigue, cold intolerance, myxedematous feature, growth retardation and constipation. Goiter was the most consistent finding in both groups and was present in all instances of spontaneously acquired primary hypothyroidism. These observations emphasize the importance of routine examination of the thyroid gland, particularly in preadolescent and adolescent girls. The finding of goiter may be the only detectable sign of hypothyroidism in the early stage of the disease. Biochemical evaluation should not be deferred because of a clinically euthyroid presentation. Replacement therapy must be instituted when findings indicate a hypothyroid state. Failure to recognize and treat hypothyroidism in these pubertal patients may compromise the adult height, since skeletal maturation will proceed under the influence of sex hormones despite the presence of hypothyroidism.