Transforming growth factor-β₁ (TGF-β₁) is a pleiotropic cytokine with a variety of effects on a wide range of cells in the immune system. Evidence suggests that TGF-β₁ is also involved in the pathogenesis of human immunodeficiency virus type 1 infections. The aim of this study was to explore possible relationships between circulating TGF-β₁ and immune as well as clinical HIV infection parameters with special impact on disease progression. TGF-β₁ concentrations were measured by ELISA in the plasma of 66 patients in different stages of HIV infection and 20 healthy controls. HIV infection resulted in a significant increase of plasma TGF-β₁ concentration compared to healthy individuals (11.4 ± 6.8 vs. 6.1 ± 1.5 ng/mL, p < 0.01). TGF-β₁ values showed a significant negative correlation with CD4 cells count (r = -0.42, p = 0.001), as well as with CD8 cells count (r = -0.031, p < 0.05). Moreover, patients with the symptomatic phase of HIV infection presented an almost twofold increase of plasma TGF-β₁ concentration in comparison to asymptomatic patients and healthy individuals. Our results demonstrate the relationship between TGF-β₁ concentrations and HIV infection advancement with marked elevation in the late stages of the disease. These findings support in vitro observations suggesting an important, immunosuppressive role of TGF-β₁ in HIV infection pathogenesis.