Objective: HIV-infected patients receiving antiretroviral treatment (ART) often present adipose tissue accumulation and/or redistribution. adipose tissue has been shown to be an HIV/SIV reservoir and viral proteins as Tat or Nef can be released by infected immune cells and exert a bystander effect on adipocytes or precursors. Our aim was to demonstrate that SIV/HIV infection per se could alter adipose tissue structure and/or function. Design: Morphological and functional alterations of subcutaneous (SCAT) and visceral adipose tissue (VAT) were studied in SIV-infected macaques and HIV-infected ART-controlled patients. To analyze the effect of Tat or Nef, we used human adipose stem cells (ASCs) issued from healthy donors, and analyzed adipogenesis and extracellular matrix component production using two dimensional (2D) and three-dimensional (3D) culture models. Methods: Adipocyte size and index of fibrosis were determined on Sirius red-stained adipose tissue samples. Proliferating and adipocyte 2D-differentiating or 3D-differentiating ASCs were treated chronically with Tat or Nef. mRNA, protein expression and secretion were examined by RT-PCR, western-blot and ELISA. Results: SCAT and VAT from SIV-infected macaques displayed small adipocytes, decreased adipogenesis and severe fibrosis with collagen deposition. SCAT and VAT from HIV-infected ART-controlled patients presented similar alterations. In vitro, Tat and/or Nef induced a profibrotic phenotype in undifferentiated ASCs and altered adipogenesis and collagen production in adipocyte-differentiating ASCs. Conclusion: We demonstrate here a specific role for HIV/SIV infection per se on adipose tissue fibrosis and adipogenesis, probably through the release of viral proteins, which could be involved in adipose tissue dysfunction contributing to cardiometabolic alterations of HIV-infected individuals.