Forty-two side impact cadaver sled tests were conducted at 24 and 32 km/h impact speeds into rigid and padded walls. The post-mortem human subjects were instrumented with accelerometers on the ribs and spine and chest bands around the thorax and abdomen to characterize their mechanical response during the impact. Load cells at the wall measured the impact force at the level of the thorax, abdomen, pelvis, and lower extremities. The resulting injuries were determined through detailed autopsy and radiography. Rib fractures with or without associated hemo/pneumo thorax or flail chest were the most common injury with severity ranging from AIS=0 to 5. Full and half thorax deflections were computed from the chest band data. The cadaver test data was analyzed using ANOVA and logistic regression. The age of the subject at the time of death had influence on injury outcome while gender and mass of the subject had little or no influence on injury outcome. Existing side impact injury criteria were evaluated such as Thoracic Trauma Index (TTI), Average Spinal Acceleration (ASA), full and half thorax deflections, chest velocity and viscous criterion, and contact force. The analysis results indicate that maximum normalized average half thorax deflection was the best predictor of AIS>/=3 and AIS>/=4 thoracic injury. TTI and upper spine accelerations were also good predictors of thoracic injury. Sixteen side impact sled tests were also conducted with the modified ES-2 dummy with rib extensions (ES-2re) under similar impact conditions as the cadaver tests. The rib extensions were added to the original ES-2 dummy ribs to prevent the "seat grabbing" action of the back plate that was noticed in some side impact vehicle crash tests with the ES-2 dummy. A separate analysis was conducted using the injury response and subject characteristics from the cadaver tests and the physical parameters derived from measurements on the ES-2re dummy in sled tests under similar conditions as the cadaver tests. This analysis provided thoracic injury criteria that could be directly applied to the ES-2re dummy. This analysis indicated subject age to have significant influence on injury outcome. Maximum rib deflection and ASA of the ES-2re were the best predictors of thoracic injury. A 50% risk of AIS>/=3 thoracic injury for a 45 year old corresponds to 44 mm (standard error range: 32 to 54 mm) of ES-2re maximum rib deflection and ASA of 46 gs (standard error range: 34 -58 gs).