Thromboembolic complications in HIV-infected patients have been reported. To our knowledge, no case-control studies have compared the prevalence of thromboembolic events between HIV-positive and HIV-negative individuals. One hundred and sixty-nine HIV-infected patients and 180 randomly selected blood donors were enrolled. Selected patients completed a specific questionnaire and were subsequently interviewed. Information was collected on family and personal history of cardiovascular disorders and the presence of personal risk factors for venous and arterial thrombosis. All reported events were adjudicated only if adequate documentation of objective tests was available. Mean age and sex were similar in the two groups. A vascular event was documented in six HIV-infected patients (3.55%) and in none of the controls (P=0.0108). Family history of cardiovascular disorders, cigarette smoking and hypertriglyceridemia were more prevalent in HIV patients than in controls. In multivariate analysis, neither family traditional cardiovascular risk factors nor HIV infection were independently associated with the presence of thromboembolic events. The results confirm the hypothesis that HIV-positive patients have an increased risk of thromboembolic disorders. Whether this increased risk has been provoked by HIV infection itself or by other associated risk factors for cardiovascular events, such as cigarette smoking and hypertriglyceridemia, remain to be clarified.