The objective of this study was to quantify the relationship between harness type and the prevalence of child restraint system (CRS) misuse. Data were collected at 21 child safety seat clinics between August, 1997 and November, 1998 in southeastern Pennsylvania and southern New Jersey. The main outcome measured was the prevalence of CRS misuse for each of the three most common harness types. Of the 438 convertible CRS evaluated, 89% demonstrated at least one form of misuse. This rate of misuse did not vary by harness type: 5-points (89%), T-shields (87%), and trayshields (93%). However specific misuses were more common for specific harness types. Having marked/ twisted harness straps was more common among five-point harnesses. T-shields were more commonly recalled, due mainly to the high market share of a particular T-shield CRS recalled for defects with the shield buckle and harness retractor mechanism. Although not statistically significant, there was a trend towards not using a chest clip when necessary in both tray-shields and T-shields when compared to fivepoint harnesses. This study confirmed a high prevalence of CRS misuse and extended previous results by demonstrating that this misuse is consistent across CRS harness designs. The data further suggest specific design improvements for each harness design based on the particular pattern of misuse.