We report a case of thrombotic thrombocytopenic purpura (TTP) in a woman infected with human immunodeficiency virus (HIV) in whose endothelial cells we detected HIV p24 antigen. The patient had an excellent response to conventional therapy for TTP and remained in complete remission 12 months after diagnosis. We also present a review of the literature on the association of TTP with HIV infection and speculate on its nature. The presence of HIV p24 antigen in the endothelial cell might be indicative of a role of virus, yet to be defined, in the pathogenesis of HIV-associated TTP.