Homocysteine (HCY) is an independent risk factor for occlusive vascular disease, the relationship of hyperhomocysteinaemia with aneurysms has not been established. The aim of this study was to assess the incidence of elevated HCY in patients with aortic aneurysms compared to controls, and patients with occlusive arterial disease. We measured HCY levels in 200 patients, 43 age- and sex-matched patients without vascular disease, 97 with aortic aneurysms (64 thoracoabdominal and 33 infrarenal) investigated for surgical intervention, and 60 patients with limb ischaemia (35 claudicants and 25 with critical limb ischaemia). Fasting blood samples were taken; serum separated and stored at −70 °C, HCY levels were measured using fluorescence polarization immunoassay (Abbott IMx® assay). Results are presented as mean ± SEM with 95 per cent confidence intervals, and the Mann–Whitney U-test was used for statistical analysis. Nine per cent of controls were hyperhomocysteineaemic (>15 µm L−1); the mean HCY level was 9.35 ± 0.64 (95 per cent CI: 8.06–10.65) µm L−1. Thirty-two per cent of the patients with aneurysms had elevated homocysteine, 13.20 ± 0.62 (95 per cent CI: 11.97–14.43) µm L−1, and 26 per cent of patients with limb ischaemia were hyperhomocysteinaemic 13.24 ± 0.68 (95 per cent CI: 11.88–14.61) µm L−1. HCY levels in both aneurysmal and occlusive disease were significantly higher than controls (P < 0.0001), and there was no difference between the occlusive and aneurysmal group. Homocysteine is prevalent in both aneurysmal and occlusive vascular disease. The treatment of hyperhomocysteinaemia is cheap, simple and inexpensive, and may represent a mechanism to modify the disease process.