Abstract
Postpartum painless thyroiditis with transient hyperthyroidism is being recognized with increasing frequency. Evidence tends to support an autoimmune cause. A 33 yr old woman who experienced typical postpartum painless thyroiditis was treated. Her sister had had a similar episode 13 yr previously, and their mother had had postpartum hyperthyroidism 42 yr earlier. This familial association apparently provides further support for autoimmunity in postpartum thyroiditis.