Endocrine and immune system explorations, systematically performed at the end of pregnancy for the last 15 years, have shown that in about 5 percent of women delivery is followed by thyroid dysfunction and goitrogenic episodes due to a painless or silent thyroiditis. In genetically predisposed subjects, this pathology is the expression of a hitherto asymptomatic chronic lymphocytic thyroiditis revealed by the generalized autoimmunity rebound that is characteristic of the postpartum period. Usually benign and transient, the thyroiditis may recur during subsequent pregnancies and eventually result in permanent hypothyroidism.