In Vehicular Ad-hoc NETworks (VANETs), some distinct characteristics, such as high node mobility, introduce new non-trivial challenges to Quality-of-Service (QoS) provisioning. Although some excellent works have been done on QoS issues in VANETs, security issues are largely ignored in these works. However, it is know that security always comes at a price in terms of QoS performance degradation. In this paper, the authors consider security and QoS issues jointly for VANETs with cooperative communications. They take an integrated approach of optimizing both security and QoS parameters, and study the tradeoff's between them in VANETs.