The present work describes an experimental study of damage to n-type silicon caused by a normal Nd:glass laser of 1.06 mu m wavelength, running in free-generation mode. Samples of different surface quality were prepared by mechanical lapping, chemical etching and polishing by fine diamond paste. This was done to study the effect of mechanical damage at the sample surface introduced during sample preparation. Damage morphology observed at different power densities shows that in the case of lapped samples the laser damage threshold is considerably lower than that of mirror-polished samples. Damage threshold results are analysed in terms of a thermal model taking into account the differences in the physical parameters of different samples and the temperature dependence of those parameters. The mechanical damage caused at the sample surface during its preparation results in an increase of surface absorptance of Si and consequently lowers its damage threshold. The evolution of damage morphology is governed by the depth of the mechanical damage.