We propose an algorithm to find piecewise linear skeletons of hand-written characters by using principal curves. The development of the method was inspired by the apparent similarity between the definitions of principal curves (smooth curves which pass through the “middle” of a cloud of points) and the medial axis (smooth curves that go equidistantly from the contours of a character image). The algorithm is an extension of the polygonal line algorithm [6, 5], originally designed to find principal curves of data sets, to compute the principal graph of a data set. Test results indicate that the proposed algorithm substantially improves the piecewise skeleton obtained by traditional thinning methods.