This paper describes the use of tip-perturbation effects in atomic force microscopy (AFM) to pattern thin films of in situ electrochemically-formed polymers. Applications of this technique to fabricate microelectrodes and junctions between the edges of very thin, dissimilar polymer films are presented. These are the first examples of spatially patterned, laterally heterogeneous polymer films having thicknesses in the 5-200-run range.