Abstract Introduction Blood samples from 733 drivers suspected of driving under the influence of alcohol in the province of Ontario from 2001 to 2005 were retrospectively examined. Methods Samples were analyzed for alcohol content by headspace gas chromatography with flame ionization detection. Drivers ranged in age from 15 to 83years old with the majority of blood samples obtained from males (n=623, 85%). Of the 704 cases where quantifiable numerical values were obtained, blood alcohol concentrations ranged from 13 to 414mg/100mL (mean 172mg/100mL) for males and 10 to 425mg/100mL (mean 173mg/100mL) for females. The majority of these drivers (n=640/704, 90.9%) had blood alcohol concentrations of 80mg/100mL and greater at the time of sampling. Analysis for alcohol was undertaken in all cases. However, additional toxicological examinations for drugs was conducted on a case-by-case basis based on the submitted case history and/or where there were requests for additional drug analysis, or where such analysis would be probative in the absence of the detection of alcohol at a concentration that could cause impairment. Results Therefore, analyses for drugs were only performed in a small subset of 42 cases (6%). Thirty-four of these cases had positive drug findings, with Δ9-tetrahydrocannabinol being the most frequently encountered drug (n=18), followed by benzoylecgonine/cocaine (n=8), morphine (n=6), lorazepam (n=5) and diphenhydramine (n=4). The majority of individuals were involved in some type of motor vehicle accident (n=658, 89.8%), with single motor vehicle accidents (n=412, 56.2%) being the most common, followed by multiple motor vehicle accidents (n=169, 23%). Injuries (n=309, 42.1%) were the main cause of individuals not being able to provide breath samples with specific, non-life threatening injuries (n=178, 24.3%) representing the highest percentage of cases. The majority of incidents (n=449, 61.3%) occurred between Friday and Sunday reaching a peak on Saturday (n=174, 23.7%). Incidents occurred throughout the day, with the majority of events (n=449/705, 63.7%) for which a time was provided occurring between 6:01 pm and 3:00 am, and the peak number of incidents occurring between 9:01 pm and midnight (n=168/705, 23.8%). Conclusion However, these data demonstrate that ‘‘drugged driving” does occur and that further, comprehensive investigation is needed to determine the frequency and type of drug use by Ontario drivers.