OBJECTIVE The effects of human immunodeficiency virus (HIV) infection on thyroid function have been reported in only a few studies with discrepant results. The aim of this study was to assess the relation between nutritional status and thyroid function in HIV infected patients.DESIGN Prospective, cross‐sectional study.SETTING A 500‐bed teaching and referral hospital serving a population of 450 000.PATIENTS Seventy‐five consecutive HIV infected patients between 21 and 40 years of age (mean 31.8 ± 0.9 years).MEASUREMENTS Nutritional status was evaluated using the body mass index (BMI), triceps skinfold thickness (TSF), mid‐arm muscle circumference (MAMC), and serum albumin concentration (SA). Hormone assays for serum T4, free thyroxine index (FTI), T3, reverse triiodothyronine (rT3), thyroxine‐binding globulin (TBG), TSH and simultaneous CD4 lymphocyte counts were determined in all patients.RESULTS Clinical stage was significantly related to nutritional status (P = 0.0001 for BMI,P = 0.0002 MAMC). The more poorly nourished groups had low mean serum T3 and rT3 levels, particularly for muscular (P = 0.0001 for T3 andP = 0.0076 for rT3) and visceral (P = 0.00001 for T3 andP = 0.0021 for rT3) protein compartments. Multivariate analysis showed that two factors, SA and MAMC, correlated significantly and independently with serum T3 and rT3.CONCLUSIONS A close relation exists between serum thyroid hormone levels and nutritional status in HIV infected patients. These patients are probably euthyroid and the abnormal findings in the thyroid function