A survey of 250 patients with insulin-dependent diabetes (IDD) holding a full motor vehicle driving licence revealed that 107 (42.8%) had not declared IDD on their application for a driving licence. 70 of these (28% of entire group) claimed that they were unaware of the statutory requirements. There was no difference in the declaration-rate between men and women. 159 patients (66%) declared IDD for their motor insurance. 86 patients (34.4%) had had severe or frequent hypoglycaemia in the preceding six months, during which they had been driving regularly. 34 patients (13.6%) admitted involvement in a driving accident since commencing treatment with insulin, and 13 of these patients were aware that hypoglycaemia had been an important causal factor. The prevalence of diabetic retinopathy and cataracts was considerable, but few patients (2.4%) had severe impairment of vision in both eyes.