In this survey we studied the prevalence of permanent hypothyroidism and prognostic factors for its occurrence 3-5 yr after postpartum thyroiditis (PPT); 54 of 120 women with PPT and 50 of 920 healthy women from among 1,040 women followed 4-5 yr earlier for PPT were recalled. Demographic information, signs, and symptoms of thyroid disorders and results of physical exams were documented. Serum T3, T4, RT3U, TSH, and anti-thyroperoxidase (anti-TPO ab) and anti-thyro-gluboline (anti-Tg ab) antibodies were measured. Twenty-two percent of the cases and four percent of the control group had permanent hypothyroidism, p<0.01. Based on the TSH level we divided the case group into two subgroups: PPT-Hypothyroidism (PPT-Hypo) and PPT-Eutyhroidism (PPT-EU); PPT-Hypo had greater titer of anti-TPO ab than PPT-Eu (437+/-283 vs 126+/-221 IU/mL, p<0.001). Comparison of mean peak serum TSH level and anti-TPO ab during the postpartum thyroiditis phase between PPT-Hypo and PPT-Eu in the case group was significant (56+/- 24 vs 23+/- 28 mU/L, p<0.001, and 1960+/-1270 vs 640+/-959 IU/L, p<0.001, respectively). Results of this survey show a high prevalence of permanent hypothyroidism following PPT in Tehran. High titers of anti-TPOAb and TSH levels at postpartum period are prognostic factors for occurrence of permanent hypothyroidism.