BACKGROUND: Thrombophilia may be associated with premature atherosclerosis, an increased susceptibility to primary arterial thrombosis and an increased failure rate for peripheral vascular or endovascular interventions. The aim of this study was to determine the prevalence of thrombophilia in patients with intermittent claudication (IC). METHODS: This was a prospective study of 116 consecutive new patients (70 men; median age 65 (range 43-84) years) referred to this regional vascular surgery unit with IC. Patients on warfarin, or who had previously undergone lower limb reconstruction and/or angioplasty, were excluded. RESULTS: Thrombophilia was demonstrated in 24 patients (21 per cent). The commonest abnormality (15 patients, 13 per cent) was a raised level of anticardiolipin antibody (ACLA) (11 immunoglobulin (Ig) M, four IgG). Other abnormalities comprised: lupus anticoagulant (one), protein C deficiency (two), protein S deficiency (two), activated protein C resistance (one) and factor V Leiden heterozygosity (three). All abnormalities were confirmed on repeat testing. No patient had a history of venous thrombosis. There was no statistically significant relationship between ACLA status and age, sex, ankle : brachial pressure index, previous myocardial infarction or stroke, previous carotid endarterectomy or coronary artery surgery, serum cholesterol, current use of antiplatelet agents or current smoking status. CONCLUSION: Almost one-quarter of new patients referred to this regional vascular unit with IC have thrombophilia; over half of those affected have a raised ACLA level compatible with the antiphospholipid syndrome. At present, the clinical significance and management implications of these abnormalities remain unknown.