As the tip in the atomic force microscope is scanned over the sample surface an image results which contains information from the sample as well as from the tip. This mainly results in an increase of the apparent size of the sample. If the tip is reasonably sharp the contribution from the tip is small. In some cases the widening still persists in spite of a very sharp tip. In this letter, a model is presented which ascribes this to the lateral forces twisting the cantilever giving an offset between the apparent point of contact and the real point of contact. This results in a shift between forward and reverse scan of the sample position in the imaging window and, if the lateral forces due to the sample and substrate are different, a change in the apparent width of the sample. ©1995 American Institute of Physics.