First global linear study of electrostatic drift waves in two realistic quasisymmetric configurations, namely the Quasi-Axially symmetric Stellarator with three fields periods (QAS3) [P. Garabian and L. P. Ku, Phys. Plasma 6, 645 (1999)] and the Helically Symmetric eXperiment (HSX) [F. S. B. Anderson , Trans. Fusion Technol. 27, 273 (1995)], are presented. Effects of the shape of the plasma on the growth rate and frequency of the ion temperature gradient (ITG) driven mode are investigated by varying the quasi-symmetric configurations to an equivalent symmetric system. The calculations have been performed using a three-dimensional (3D) global gyrokinetic code in the magnetic configurations provided by the magnetohydrodynamic (MHD) equilibrium code VMEC [S. P. Hirshman and D. K. Lee, Comput. Phys. Commun. 39, 161 (1986)]. The plasma is modeled by gyrokinetic ions and adiabatic electrons. In QAS3, results are very close to those obtained for a tokamak. The drift waves are only slightly affected by the shape of the plasma or the local magnetic shear. On the other hand, results for the HSX configuration show a clear 3D effect, namely a strong toroidal variation of the drift wave mode structure. This variation is a clear structure of the 3D plasma shape. However, first results show that the growth rate of the ITG driven mode is largely unaffected by this effect. (C) 2001 American Institute of Physics.