We have studied risk factors for diabetic foot ulceration by comparing diabetic patients who had active foot ulcers (n = 86) with diabetic patients who had no history of foot ulcers (n = 49). Whereas there was a strong association of diabetic foot ulceration with abnormal vibratory perception (Odds Ratio = 10.77; p less than 0.001, which increased with worsening vibratory perception), there was little association with abnormality of the ankle-pressure index (Odds Ratio = 2.84, p = n.s.). Although foot ulceration and limited joint mobility were associated (Odds Ratio = 3.57, p less than 0.001), this relation was not significant when allowances for abnormal vibratory perception and diabetes duration were made. These data suggest that sensory neuropathy is of greater aetiological importance than peripheral vascular disease in the development of diabetic foot ulceration. The measurement of the vibratory perception threshold is clinically useful in identifying those diabetic patients at high risk of foot ulceration.