A comprehensive stability analysis of the ion‐temperature‐gradient‐driven mode in various parameter domains is presented. The effect of parallel ion dynamics on the threshold value in toroidal geometry is investigated for the short‐wavelength and finite‐shear limits. A general explicit expression for the threshold is given, which is in agreement with the results obtained by solving the full integrodifferential equation. The destabilizing effect of trapped electrons below the threshold is qualitatively similar to the results of local theory, but electron collisionality has to be sufficiently weak. In the long‐wavelength limit, two branches exist, respectively, toroidal and slablike in character. The toroidal branch has been investigated elsewhere [Romanellietal., Phys. Fluids B3, 2496 (1991)]. In this paper, the stability of the slablike branch is studied both analytically and numerically. The trapped‐ion effects on the threshold are discussed in detail.