BACKGROUND Despite the high prescription rate of benzodiazepine-like hypnotics (z-hypnotics), there is limited information on the road traffic accident risk associated with the use of these drugs. We wanted to investigate whether filling a prescription for zopiclone or zolpidem was associated with increased risk of road traffic accidents at a national population level. Nitrazepam and flunitrazepam were used as comparator drugs. METHODS All Norwegians 18-69 years (3.1 million) were followed-up from January 2004 until the end of September 2006. Information on prescriptions, road traffic accidents and emigration/death was obtained from three Norwegian population-based registries. The first week after the hypnotics had been dispensed was considered to be the exposure period. Standardized incidence ratios (SIRs) were calculated by comparing the incidence of accidents in the exposed person-time to the incidence of accidents in the unexposed person-time. RESULTS During exposure, 129 accidents were registered for zopiclone, 21 for zolpidem, 27 for nitrazepam and 18 for flunitrazepam. The SIRs were (SIR for all ages and both sexes combined; 95% CI): z-hypnotics (zopiclone+zolpidem) 2.3; 2.0-2.7, nitrazepam 2.7; 1.8-3.9 and flunitrazepam 4.0; 2.4-6.4. The highest SIRs were found among the youngest users for all hypnotics. CONCLUSIONS This study found that users of hypnotics had a clearly increased risk of road traffic accidents. The SIR for flunitrazepam was particularly high.