The pre-amorphization damage structure in high-energy ion-implanted Si was studied to better understand the processes that eventually lead to the formation of a continuous amorphous layer. Different kinds of defect structures would induce different deformation in the host lattice. In this paper we report the results of a systematic study on the dependence of the strain profile on the local defect density in nitrogen implanted silicon [100] crystals. The study was carried out as a function of the ion fluence for three different implantation conditions: random incidence, and channelling. The results of some preliminary low-temperature (up to 300°C) annealing experiments are also reported. The linear dependence of the strain upon the defect concentration is confirmed by the present results. The extremely low value of the proportionality factor is discussed in terms of possible formation of amorphous clusters …