The course of human immunodeficiency virus infection and the acquired immunodeficiency syndrome can be complicated by a variety of endocrine abnormalities. This article describes the findings of a prospective autopsy study of the thyroid in 100 patients who died of complications of AIDS before the advent of the so-called highly active antiretroviral therapy [corrected]. A wide range of bacterial, fungal, viral, and neoplastic disorders were observed. Mycobacterium tuberculosis was recorded in 23% of the patients, cytomegalovirus in 17%, Cryptococcus in 5%, Mycobacterium avium in 5%, Pneumocystis in 4%, and other bacteria or fungi in 7%. Kaposi's sarcoma was recorded in 2% of patients and occult papillary carcinoma in 4%. Four patients had dual infections of the thyroid. The mean weight of the thyroid was lower than normal, and 1 case of thyroid follicular atrophy is presented. A review of the medical literature on thyroid disorders in HIV-infected patients is included. Physicians caring for HIV patients should be aware of the possibility of thyroid dysfunction in their patients.