Thrombosis of upper extremity arteries is most commonly due to atherosclerosis of the proximal subclavian artery, trauma, or catheter-related injury. In the absence of an identifiable cause, a search for a hypercoagulable state is indicated. Hematologic manifestations of human immunodeficiency virus (HIV) infection and AIDS are frequent occurrences (Coyle TE. Med Clin N Am 1997;81:449-476). The most important of these are cytopenias (anemia, neutropenia, and thrombocytopenia). The incidence and severity of cytopenia are generally correlated to the stage of the HIV infection. In addition, various coagulation abnormalities have been reported in HIV-infected patients. Apart from thrombocytopenia, these have included a prolonged APTT due to the presence of lupus anticoagulant, an increased prevalence of protein S and heparin cofactor II deficiency, and hypoalbuminemia-related fibrin polymerization defects (Toulon P. Ann Bio Clin (Paris) 1998;56:153-160). HIV infection has also been associated with endothelial dysfunction. Although for the most part asymptomatic, elevated D-dimer levels have been found in HIV-infected patients, suggesting the existence of a prethrombotic state. In fact, clinical thrombosis eventuates in 2% of these patients (Toulon, 1988). Documented thromboses have involved both veins and arteries. We hereby present a patient who developed an acute thrombosis of his brachial artery as the initial manifestation of HIV infection. Am.