In our article Self-monitoring of blood glucose in diabetes (DTB 2007; 45: 65–9), we suggested that patients who drive and take insulin should test their blood glucose before driving, and at intervals (e.g. every 2 hours) on long journeys; should carry a blood glucose testing meter and carbohydrate in their vehicle; and should wait at least 30 minutes after treating an episode of hypoglycaemia before restarting driving. We offered this advice because hypoglycaemia associated with insulin therapy can impair driving performance, and symptoms alone (e.g. subjective feelings of weakness) are a poor …