This paper presents a new technique to perform automatically the 3-D registration of two 3-D scanner images. The aim is to compute the rigid geometric transform existing between two views of the same object, taken into two different positions. The basis of our method is to extract characteristic 3-D lines from the two images, called crest lines, and to compute the geometric transform that map one of the set of lines onto the other one. Our method is fully automatic. It is also very fast and robust, because the crest lines set is a very compact and stable representation of the principal geometric information of a 3-D image. We present in this paper the example of an automatic registration performed with two 3-D images of a skull.