The initial positioning of anthropomorphic test devices (ATDs) can influence the outcomes of crash tests. Current procedures for positioning ATDs in rear seats are not based on systematic studies of passenger postures. This paper compares the postures of three side-impact ATDs to the postures of 24 men and women in three vehicle rear seats and 16 laboratory conditions. When positioned using current procedures, the locations of the ES-2 and SID-HIII ATD heads are generally rearward of those observed with similar-size passengers. The SID-IIs head locations matched the expected locations of heads of passengers of similar size more closely. As the seat back angle was increased, people reclined less than the ATDs. Based on these findings, a new ATD positioning procedure for rear seats was developed. The primary objective of the new procedure is to place the ATD head in the location that is most likely for people of similar size. Linear regression equations specify the fore-aft location of the ATD hips and head with respect to the seat H-point as a function of seat back angle (SAE A40) and seat cushion length. The new procedures have been tested with the SID-HIII, ES-2, and SID-IIs side impact ATDs, but are also applicable to frontal impact testing.