The ability to measure six degree of freedom head kinematics in impact conditions (i.e. motor vehicle crashes and sport activities) plays an important role in injury assessment of the head/neck complex. Potential accuracy of head instrumentation schemes have recently been improved by using advanced angular rate sensors, so in this study an instrumentation technique for obtaining accurate head kinematics in impact conditions using an external fixture is proposed and validated. The methodology proposed in this study utilizes six accelerometers and three angular rate sensors (6aω) on a lightweight tetrahedron fixture (t6aω) originally designed for measuring head kinematics of post mortem human surrogates (PMHS) in car crash scenarios using a nine accelerometer array package (NAAP) configuration (tNAAP). A Hybrid III 50th percentile male anthropomorphic test device (ATD) head containing an internal nine accelerometer array package (iNAAP) was used to validate the t6aω method proposed in this study. The t6aω instrumentation was installed on a tetrahedron fixture which was attached externally to the Hybrid III ATD head, tested in direct contact tests of various severities, and then compared to data measured from the iNAAP of the Hybrid III ATD head which provided the kinematics gold standard to validate the proposed technique. Results indicate that angular acceleration obtained from the t6aω scheme was comparable to that determined from the iNAAP scheme in the head impact conditions, showing normalized root mean squared deviation (NRMSD) values less than 5%. Transformed linear acceleration from the t6aω to the center of gravity (CG) of the Hybrid III ATD head was also comparable to acceleration measured directly from the accelerometers at the CG, exhibiting less than 5% NRMSD. Accurate angular acceleration and velocity are important to obtain accurate transformed acceleration. Since the t6aω angular acceleration component of the transformed linear acceleration at an inaccessible point was shown to have equivalent accuracy to iNAAP (less than 5% error), and the angular velocity component of t6aω instrumentation should be more accurate than the tNAAP scheme (since it is directly measured by the ARS as opposed to using numerical integration as in tNAAP), the t6aω scheme should yield more accurate transformed linear acceleration at an inaccessible location than the tNAAP scheme. The proposed instrumentation should aid in the development and evaluation of head, neck and brain injuries in future testing.