For low-speed rear-end impact tests, the recently developed Biofidelic Rear Impact Dummy (BioRID) is more human-like compared to the Hybrid III. In the current study, three-dimensional mathematical Multi Body System models in MADYMO of the BioRID I and of four car seats were developed and validated. A sensitivity analysis was designed to verify the stability of the mathematical models, and showed that among the dummy parameters that influenced the BioRID I performance, the curvature of the thoracic and cervical spine had the highest influence. Among the seat parameters, the recliner characteristic and the head-restraint position had the most influence on the BioRID I performance. The MADYMO BioRID I is a useful tool for parameter studies in crash-safety research and development. An advantage of the models is their similarity to mechanical counterparts, which allows comparison with crash tests.