In a six-year survey of 5,179 school children in Arizona, Utah, and Nevada 62 cases of chronic lymphocytic thyroiditis were identified giving a prevalence of 1.2%. Thyroids were enlarged in 85%, firm in 60%, and had an irregular or lobulated surface in 75%. Antibodies to thyroglobulin were demonstrable in the serum at some time during the course of the disease in 76% by the tanned red blood cell technique and in 93% by radioimmunoassay. Serum TSH concentrations were elevated in seven of 15 subjects. Many of the cases were early or mild thyroiditis and, in most instances, subjects were asymptomatic and considered clinically euthyroid. Two subjects were hypothyroid, and two appeared clinically hyperthyroid. Spontaneous resolution of thyroiditis occurred in 15 of 32 individuals who received no treatment. Resolution occurred in 14 of 30 children treated with thyroid hormone supplement. The results suggest that lymphocytic thyroiditis in children may be present without symptoms and in many is a self-limiting disorder from which complete recovery occurs spontaneously.