Ion‐implantation damage has been studied in thin reeds of silicon by resonant‐frequency and internal‐friction measurements. For a dose of 1016/cm2of28Si+, the principal effects are the appearance of an internal‐friction peak and a decrease in the flexural vibration frequencies. The amorphous surface layer produced by implantation is deduced to have a Young's modulus of 1.24×1012dyn/cm2and a density of 0.95 of the crystal density. The internal stress in the amorphous layer has been measured and found to be far smaller than that corresponding to a purely elastic accommodation of the density change.