both the youngest and oldest drivers in our society are overrepresented amongst fatal crashes. as such, there is a need for prevention strategies which may reduce crashes in each cohort. passenger presence is one factor that has been shown to be both an obstruction and an aid in reducing fatal crashes. this study aimed at determining which types of passenger characteristics and driving conditions benefited either teen (16-19 years of age) or elderly drivers (65 years of age or older). the effects of passengers in fatal crashes in the pars database through 1975-2003 were examined. results showed that whether a passenger was useful for various age groups differed for driving circumstances both inside and outside of the vehicle. overall elderly and middle age drivers experienced a protective effect for the presence of a passenger whereas teen drivers experienced an increase risk for unsafe driving behaviours when a passenger was present. an analysis of gender and age of both passenger and driver suggested that the relationship of these variables might be an important consideration. it was also found that certain situational variables such as weather and time of day may moderate the degree to which a passenger is effective. implications of these findings are discussed.