Postpartum thyroiditis (PPT) is a common condition that can occur in the first 12 months after delivery, affecting 5% to 7% of all postpartum women. This article provides a case illustration of this disorder. The typical clinical course for PPT is that of initial thyrotoxicosis (hyperthyroidism), followed by a hypothyroid state, and eventual return to normal thyroid function. Symptoms of thyroid dysfunction can be mistaken for normal postpartum adjustment and fatigue by the patient. PPT must be distinguished from other causes of abnormal thyroid function. Treatment focuses on reduction of symptoms. Antithyroid medication is not indicated. Women who develop PPT are at high risk for future development of hypothyroidism. © 2008 American College of Nurse Practitioners.