The response of the human head and neck to impact acceleration has been previously reported for the -X (chest to back) and +Y (right to left) directions. Wide ranges of sled peak acceleration, rate of onset of acceleration and duration of acceleration have been investigated and reported. A major mechanical effect on the dynamic response due to initial position for the -X direction has been reported. The purpose of this study is to report the initial position effect on the human head and neck response for +Y direction experiments.Four initial positions of the head relative to the first thoracic vertebral body (T1) have been investigated over a range of sled acceleration peaks from 2 to 7G. The data from six young adult male volunteers representative of a wide range of anthropometry will be presented. There are 18 experiments for each volunteer for a total of 108 experiments.The effect of initial position on the resulting head angular and linear acceleration, velocity and displacement will be presented. A comparison of the initial position effect for -X and +Y direction experiments will be made. The ability to model the initial position effect will be discussed.