OBJECTIVE: We test the hypotheses that the implementation in Denmark of new, stricter European Union (EU) legislation on driver's licensing, with the purpose to improve traffic safety in January 2012, has reduced the self-reported rate of severe hypoglycemia in a routine clinical setting and that anonymous reporting results in higher event rates.

RESEARCH DESIGN AND METHODS: A cohort of 309 patients with type 1 diabetes was recruited in the outpatient clinic at Nordsjællands University Hospital Hillerød, Denmark. Yearly numbers of severe hypoglycemic events defined by need for treatment assistance from another person were retrieved from medical records in the years 2010 to 2012 and retrospectively reported in an anonymous questionnaire. Data from medical records in 2012 were compared with those from 2010 and 2011 and with data from the questionnaire.

RESULTS: Reported rates of severe hypoglycemia in the medical records were reduced by 55% in 2012 compared with the prior years (P = 0.034). The proportion of subjects reporting recurrent episodes was grossly reduced from 5.6 to 1.5% (P = 0.014). Compared with anonymous reporting in the questionnaire, the rate of severe hypoglycemia in 2012 was 70% lower (P < 0.001).

CONCLUSIONS: Reporting of severe hypoglycemia by patients with type 1 diabetes is significantly reduced following implementation of EU driver's licensing legislation that implies withdrawal of driver's licensing in case of recurrent episodes within 1 year. The resulting burden of concealed severe hypoglycemia may impair the safety of affected patients and unintentionally paradoxically reduce the general traffic safety.