Clinical and laboratory characteristics of 224 patients with thyroidal infection reported since 1900 are reviewed. Much of the prior literature on this subject has assumed that most instances of thyroiditis are infectious and that all lymphomatous thyroiditis is tuberculous. Similarly, thyroiditis occurring with syphilis was often equated with treponemal invasion of the gland. Acute bacterial thyroiditis is rapid in onset and more likely than tuberculous infection to produce fever, pain, and tenderness. Suppurative and mycobacterial infections are most common among women with preexisting thyroid disorders. Mortality due to infectious thyroiditis is lower in cases covered by this review than has been previously reported. Gummatous and fungal infections of the thyroid are generally diagnosed only at biopsy or necropsy. Frequent thyroidal involvement in disseminated aspergillosis warrants careful investigation of the gland in patients with this infection. Echinococcosis of the thyroid is a chronic process that is generally diagnosed only following excision.