Two hundred and seventy seven Saudi women were prospectively evaluated post-partum to determine the frequency of post-partum thyroiditis. Four to six weeks after delivery, 12 (4.3%) had positive antimicrosomal antibodies and 8 (2.9%) had positive antithyroglobulin antibodies. At 6-8 weeks post-partum, out of 82 subjects followed up, 4 (4.9%) had positive antimicrosoMal antibodies and 1 (1.2%) had positive antithyroglobulin antibodies. At 8-12 weeks post-partum, out of 70 subjects, antimicrosomal antibodies were detected in 5 (3.5%) subjects and antithyroglobulin in 2 (1.4%). Their routine thyroid function tests (T3, T4, and TSH) remained within the normal range. There was no clinical evidence of hyper- or hypothyroidism in any of the patients during the follow up. Post-partum thyroiditis, appears to be relatively uncommon in Saudi Arabia. It does not produce any clinical illness or cause significant subclinical thyroid dysfunction.