The aim of this cross-sectional multicenter study was to determine the prevalence of and risk factors for hypothyroidism in human immunodeficiency virus (HIV)-infected patients. Free T4, free T3, and thyroid-stimulating hormone levels were determined. Data on age, sex, weight variation, smoking status, duration of HIV infection, Centers for Disease Control and Prevention disease stage, CD4 cell count, HIV RNA load, lipodystrophy, HIV-hepatitis C virus coinfection, and antiretroviral treatment (type of drugs and total cumulative dose) were collected. The prevalence study included 350 HIV-infected patients. Sixteen percent of patients had hypothyroidism: 2.6% had overt hypothyroidism, 6.6% had subclinical hypothyroidism, and 6.8% had a low free T4 level. The prevalence of subclinical hypothyroidism was higher among HIV-infected men than among HIV-infected women. A case-control study was conducted that compared hypothyroid (n=56) and euthyroid (n=287) patients. In the multivariate analysis, receipt of stavudine and low CD4 cell count were associated with hypothyroidism. Therefore, screening may be indicated for patients, especially men, who have received stavudine or have decreased CD4 cell counts.