Patients infected with the human immunodeficiency virus (HIV) appear to have a high risk of ischaemic cerebral events. We observed two cases of cerebral infarction in patients with acquired immune deficiency syndrome (AIDS). In the first case, a 38-year-old homosexual with no cardiovascular risk other than smoking presented with rapidly progressive hemiparesia. Brain CT-scan visualized two infarcts in the territory of the right sylvian artery and the arteriography an occlusion of the internal carotid artery. In the second, a 37-year-old homosexual, hospitalization was required for a left-sided pure sensitive epilepsy seizure. There was no cardiovascular risk other than smoking. Magnetic resonance imaging showed parietal ischaemia and thrombus in the left atrium without atrial hypertrophy was seen at transoesophageal echocardiography. In both cases, there was no evidence of endocarditis, dissection of the neck vessels or disseminated intravascular coagulation nor of associated viral or bacterial infectious complication of AIDS. Angiographic findings eliminated cerebral vascularitis. Among the perturbed haemostasis factors previously reported in HIV+ patients, we observed free proteins S deficiency (68 and 43%) and heparin cofactor II deficiency (54 and 40%). Serum albumin was 33 and 32 g/l respectively. Outcome was favourable in both cases with anticoagulant therapy. These coagulation anomalies would not appear sufficient to explain cerebral infarction. Other mechanisms including immune complexed deposition, direct HIV toxicity for endothelial cells or the effect of cytokines on smooth muscles fibres and fibroblasts are probably more important causal factors.