Subacute thyroiditis is a common disease that often goes undetected. Indeed, both painful and painless thyroiditis are easily overlooked or misdiagnosed and perhaps mistreated unless careful attention is paid to the patient's history and physical examination. Treating the hyperthyroidism of subacute thyroiditis as if it were Graves' disease, for example, would be inappropriate, since therapy for the two entities is completely different. A form of painless thyroiditis, for reasons that remain unclear, can occur in the postpartum period and may be related to postpartum psychosis or depression.