Stability limits of highly elongated, D-shaped plasmas have been measured in the TCV (tokamak a configuration variable) tokamak. It is found that the plasma current is limited by kink-type disruptions, preceded by magnetohydrodynamic (MHD) mode activity. The mode structure has been analyzed using magnetic fluctuation and soft x-ray diagnostics. Mode numbers, growth rates, and experimental stability limits are consistent with ideal and resistive MHD models, based on measured plasma shapes and profiles. These results provide the first experimental confirmation of previously predicted stability limits at high elongation, kappa less than or equal to 2.58.