PURPOSE:The clinical course in adult autoimmune thyroiditis varies: both transient and intermittent hypothyroidism occur during the course of disease and spontaneous recoveries from the hypothyroid state has been described. To determine whether these kinds of variations occur in the course of juvenile chronic lymphocytic thyroiditis and whether the size of thyroid gland, or immunologic measurement such as thyroid antibodies correlated with the course or outcome of juvenile chronic lymphocytic thyroiditis. METHODS:Fifty six patients (54 girls) who attended the clinic between 1986 and 1996 were followed during 36 months prospectively. The clinical diagnosis of juvenile chronic lymphocytic thyroiditis was confirmed by Fisher et al.(1975) criteria in all patients. Assessment of thyroid function was based on clinical diagnosis and on the levels of thyroid stimulating hormone and free thyroxine. Physical examination, thyroid function test and antithyroid antibody test were evaluated with 6 months intervals. RESULTS:Initially, 27 patients were euthyroid, 19 compensatory hypothyroidism and 10 overt hypothyroidism. At the end of follow up, 31 patients were euthyroid, 11 compensatory hypothyroidism and 14 overt hypothyroidism. On one or more occasions, 92.7% of the patients had positive results for thyroid antibodies. Overt hypothyroidism at the end of follow up correlated with the initial thyroid states and with detection of thyroglobulin antibodies. CONCLUSIONS:The best predictors of the final hypothyroid state were initial hypothyroidism and detection of thyroglobulin antibodies.