Stimulated emission was studied using time-integrated and time-resolved photoluminescence in ZnO comb, tetrapod, and rod nanostructures. All the measurements were performed on ensembles of the nanostructures. The nanostructures were fabricated by vapor deposition (combs, tetrapods) and hydrothermal methods (rods). While stimulated emission was detected in all of the nanostructures, significant differences in the behavior of the stimulated emission, as well as the lasing threshold power, were found for different morphologies. The differences in the time evolution of the lasing spectra were particularly pronounced. The observed differences in the stimulated emission spectra of the three types of nanostructures in both exciton-exciton scattering and electron-hole plasma regimes are discussed.