The aim of this study was to estimate the association between diabetes and its complications and at-fault automobile crashes among older drivers. This was a population-based case-control study. Case subjects were drivers aged > or = 65 years who had been involved in a crash during 1996 in which they were at fault. Two control groups were selected: 1) crash-involved not-at-fault subjects and 2) non-crash-involved subjects. Telephone interviewers collected information on demographic characteristics, driving habits, diabetes sequelae and treatment, other chronic medical conditions, and visual function. Overall, there was no association between diabetes and at-fault crash involvement. The adjusted odds ratio (OR) for diabetes was 1.1 (CI 0.7-1.9) when case subjects were compared with either control group. However, the adjusted OR for diabetes was 2.5 (0.9-7.2) among subjects who had been involved in a crash in the 4 years preceding 1996, while it was only 0.9 (0.5-1.7) among those who had not. There was no evidence of an association between treatment modalities and at-fault crash involvement. Case subjects were, although not significantly (P = 0.25), more likely (OR 2.4) to report neuropathy compared with both control groups, and retinopathy was not associated with increased crash risk. This study provides no evidence that older drivers with diabetes are at increased risk for automobile crashes. There remains the possibility that those with diabetes who have more severe disease or have had multiple crashes are at increased risk.