This paper presents a new needle path planning method for the insertion of rigid needles into deformable tissue. The needle insertion point, needle heading, and needle depth are optimized by minimizing the distance between a rigid needle and a number of targets in the tissue. The optimization method is based on iterative simulations performed using a tissue finite element model. At each iteration, the best 3-D line fitted to the displaced targets in the deformed tissue is used as a candidate for a new insertion line. First, this method is implemented in a prostate brachytherapy simulator under different boundary conditions to minimize the targeting error. It is shown that the optimization method converges in a few iterations and decreases the seed misplacement error to less than the needle diameter. Second, the efficacy of the optimization algorithm is verified by optimizing the insertion parameters for a brachytherapy needle before insertion into a prostate tissue phantom. The elastic properties of the phantom and the needle-tissue interaction parameters were identified in an independent experiment. The optimization algorithm is effective in decreasing the targeting error.