The objective of this paper is to provide a first approach to hybrid structures optimization. A given shell structure of an automotive BIW is affected by two load cases, which are calculated separately so the particular needs in the BIW from each load case can be easily identified. The BIW is composed of a proposed composite cabin and a metal alloy motor and rear compartment, providing in this way a very reliable, affordable and light structure. An introductory test with Topological optimization is performed to the full body structure, in order to assess where the main stress concentrations are. All of this during normal driving and a single crash situation. Topometric and Sizing optimization is used for the thickness and fiber angle in the composite Cabin structure. Road loads applied to the frontal and rear strut towers are taken as load cases. The angle and thickness optimization halves the minimum mass required to fulfill the constraints, in comparison with just thickness optimization.Finally a Topometric and Topographic optimization for thickness and shape for the front midrails under a frontal crash situation is performed. This part undergoes a dynamic impact as a load case. The front part of the BIW is separated from the rest of vehicle and ESL (Equivalent static loads) are applied. This is performed with the joint process of DS Genesis and LS-DYNA. The optimized form of the midrails obtained is much lighter and stronger than the original, maintaining appropriate size and dimensions in the original packaging configuration.