Postpartum thyroiditis (PPT) is the occurrence, in the postpartum period, of transient hyperthyroidism and/or transient hypothyroidism, with most women returning to the euthyroid state by 1 year postpartum. The prevalence of PPT varies from 1.1 to 16.7%, with a mean prevalence of 7.5%. Women with type I diabetes mellitus have a three-fold increase in the prevalence of PPT. PPT is an autoimmune disorder which is a transient form of Hashimoto's thyroiditis occurring postpartum as a consequence of the immunologic flare following the immune suppression of pregnancy. Women experience symptoms in both the hyperthyroid and hypothyroid phase, but the association between PPT and postpartum depression remains undefined. Approximately 25% of women with a history of PPT will develop permanent hypothyroidism in the ensuing 10 years. Treatment for the hyperthyroid phase, when required, is a short dose of beta-blockers. Women with a TSH greater than 10mU/l, or between 4 and 10mU/l with symptoms or attempting pregnancy, require thyroid hormone replacement. Whether or not to screen for PPT remains controversial.