Thrombotic thrombocytopenic purpura (TTP) is a syndrome characterised by the clinical pentad of microangiopathic haemolytic anaemia (MAHA), thrombocytopenia, renal failure, fluctuating neurologic signs, and fever. The aetiology of TTP is unknown, but associations with various underlying diseases, infections and drugs have been identified. One of these associations is with HIV infection. We describe the clinical picture, the laboratory results and the response to plasma therapy of two cases of HIV-associated TTP. In both patients, a longitudinal semiquantitative assessment of the numbers of schistocytes in blood was made, which correlated well with the more traditional parameters of disease activity. Since 1987, at least 49 patients with HIV-associated TTP have been reported. A case-analysis of the 38 patients who were described in sufficient detail and a review of the literature in the setting of HIV infection is presented. The most important conclusions from these combined data are: (1) TTP usually seems to occur in patients with a CD4+ lymphocyte count < 250 x 10(6).l(-1); (2) more than 50% of the patients present with TTP soon after or during an infectious or malignant disease; (3) plasma exchange is the therapy of choice, still resulting in mortality of 22%; (4) higher initial platelet count and creatinine level are correlated with an adverse outcome.