This paper provides new insight into the situational risks of young drivers, especially in terms of the passenger effect. Two 1988 data bases from the Ontario Ministry of Transportation were used to estimate accident involvement rates by number of passengers, time of day and day of the week--first individually and then for all two-way combinations with the passenger variable. Accident data were derived from police reports for all accidents involving a fatality, personal injury or property damage exceeding $700. Estimates of exposure were based on the most up-to-date provincial travel survey available at the time of the study. Results indicate that the accident involvement rates of 16-19 year old drivers are higher than those of 20-24 and 25-59 year olds in all situations that were examined, but that they were disproportionately high on weekends, at nighttime and with passengers. The results of the passenger variable are particularly interesting because, unlike weekends and nighttime, the negative effect of passengers on overall accident rates was evident only for 16-19 year old drivers. This effect was quite pronounced for both sexes, with accident involvement rates being approximately twice as high with passengers as without. For 16-19 year olds, accident rates were also significantly higher for two or more passengers versus one passenger. The highest rates for this age group occurred with passengers at nighttime. Possible explanations for these patterns and policy implications are discussed.