A three-stage model to explain how the secondary defects consisting of interstitial dislocation loops evolve from the primary defects in ion-implanted silicon is presented. Crystals implanted to an ion dose belowDc(critical dose which forms a continuously damaged layer), such that the primary damage clusters do not overlap, were studied. The model suggests that the Frenkel pairs formed by ion impact produce submicroscopic clusters of vacancies and interstitials which are stable up to about 900 K. Upon heating to a higher temperature the smallest interstitial clusters emit mobile interstitials and/or the vacancy clusters emit mobile vacancies. The larger clusters grow and convert to dislocation loops. Vacancy loops shrink and disappear; interstitial loops grow because of the excess of interstitial'. The total area per unit area of interstitial loops remaining after a high temperature anneal above 1100 K corresponds to the number per unit area of the implanted atoms. The implication of this is that for vacuum and dry nitrogen anneals the surface is not important as a sink or source for point defects and that the annealing processes occur almost entirely within the buried damaged region.