Due to unique mechanical properties (e.g. superelasticity) and excellent biocompatibility, NiTi shape memory alloys (SMA) are utilized in many medical applications as surgical tools or reinforcement for arteries and veins (stents) [1]. The need of realistic simulations of these components demands precise description of constitutive behavior of NiTi alloys. The complex behavior of NiTi stems from multiple deformation mechanisms, which come into the play simultaneously - elasticity, phase transformations, reorientation of martensite. Too simplified description of such phenomena, neglecting e.g. R-phase transition or material anisotropy due to texture may lead to unsatisfactory numerical simulations and, consequently, to erroneous predictions concerning reliability or life time of applications