Two types of biaxially oriented poly(ethylene terephthalate) film have been examined using scanning force microscopy (SFM). For Mylar D, a material containing silicate surface additives, non-contact-mode and single scan contact-mode SFM were found to yield essentially similar topographical data. At elevated loads, contact-mode SFM results in the direct modification of sample topography. Ridged structures were observed to form following repeated scanning of both materials at increased contact force. Generally, damage was significant at loads > 10 nN; however, repeat scanning (five times) was found to cause wear at loads as small as 2 nN. Lateral force microscopy revealed that the debris which accumulated along the perimeter of the worn region exhibited a high frictional response. We speculate that this debris results from the displacement of low-molecular-weight material or polymer chain fragments. Tip-induced wear under liquid led to the formation of worn regions with a smooth morphology. The wear mechanisms in operation during contact-mode SFM at loads greater than 10 nN probably include both mechanical deformation and adhesion components.