The damage and strain induced by irradiation of both relaxed and pseudomorphic GexSi1-x films on Si(100) with 100 keV 28Si ions at room temperature have been studied by MeV 4He channeling spectrometry and x-ray double-crystal diffractometry. The ion energy was chosen to confine the major damage to the films. The results are compared with experiments for room temprature Si irradiation of Si(100) and Ge(100). The maximum relative damage created in low-Ge content films studied here (x=10%, 13%, 15%, 20%, and 22%) is considerably higher than the values obtained by interpolating between the results for relative damage in Si-irradiated single crystal Si and Ge. This, together with other facts, indicates that a relatively small fraction of Ge in Si has a significant stabilizing effect on the retained damage generated by room-temperature irradiation with Si ions. The damage induced by irradiation produces positive perpendicular strain in Ge xSi1-x, which superimposes on the intrinsic positive perpendicular strain of the pseudomorphic or partially relaxed films. In all of the cases studied here, the induced maximum perpendicular strain and the maximum relative damage initially increase slowly with the dose, but start to rise at an accelerated rate above a threshold value of ∼0.15% and 15%, respectively, until the samples are amorphized. The pre-existing pseudomorphic strain in the GexSi1-x film does not significantly influence the maximum relative damage created by Si ion irradiation for all doses and x values. The relationship between the induced maximum perpendicular strain and the maximum relative damage differs from that found in bulk Si(100) and Ge(100).