Predictions of occupant motion in passenger vehicles undergoing rollovers have been hampered by the uncertainties of the vehicular motion. These uncertainties arise due to a host of factors which may be difficult to quantify, such as trip conditions, vehicle/terrain interaction dynamics and mass eccentricities. In this paper the initial segment of a roll sequence of high angular velocity (greater than 4 radians per second) about a longitudinal axis is examined. The resultant unrestrained motions of the near and far side occupants are studied. To facilitate this analysis a mathematical model has been developed which incorporates dynamic characteristics of the occupant, the vehicle and the terrain surface. The analysis is carried through the first significant vehicle/ground impact following roll initiation. Occupant kinematics are described.