Acute emphysematous thyroiditis is a severe pyogenic infection of the thyroid gland characterized by the production of gas. Although earlier writers of the pre-antibiotic era had referred to 'gangrene of the thyroid with gas formation' (1-3), only 5 cases of gas-forming or emphysematous thyroiditis have been specifically documented. In this report, the sixth case of acute emphysematous thyroiditis is presented and the clinical features of this rare but potentially lethal infection of the thyroid gland are described. The pathogenesis and management of the disease are discussed.