We report two cases of chronic autoimmune thyroiditis, one patient with recurrent painless thyroiditis and another with recurrent postpartum thyroiditis. In these two patients, the episode of subacute thyroiditis seemed to be immune mediated. Thyroid ultrasonography showed a diffuse, markedly hypoechogenic gland, coinciding with each of the episodes of transient thyroid dysfunction that reverted to a normal echographic appearance with recovery of normal thyroid function. These two cases show that a diffuse low echogenicity of the thyroid, frequently seen in autoimmune thyroid disorders, can be a reversible event and suggest that the transient nature of certain forms of hypothyroidism may be predicted by a follow-up echographic examination. Further studies with a larger number of patients are required to confirm this observation.