When designing and optimizing spatial flexure mechanisms, it is hard to predict collision due to 3D motion and large deformations, which compromises the utilization of spatial freedom. A computationally efficient collision test is desirable to assure that feasible mechanism designs are found when algorithmically optimizing the shape of elastic mechanisms, which are prone to collision. In this paper, a method is presented to test for collision specifically suited for flexure mechanisms by taking advantage of the typical slender aspect ratio and shape of the elastic members. Hereby, an efficient collision test is obtained that allows for the computation of a quantitative value for the severeness of collision. This value can then be used to efficiently converge to collision free solutions without excluding good mechanism designs leading to improved mechanisms, which utilize the maximum spatial design freedom.