We present a personal casuistic of 18 cases of pilomatrixoma. We make a reference of the clinical and histological situation of our patients. We remind that even if it isn't a frequent pathology, it possesses however, in almost every cases, certain characteristics very typical that permit to arrive to a correct diagnosis. We bring out a sign that made possible this diagnosis: the palpation of a tumor with a rocky consistency where united planes forming salient angles like a stone with many facets are evident: "Faceted stone sign". All the cases were treated surgically with complete extirpation of the tumor and up to now we haven't observed any relapses. The palpation of the sign of the "faceted stone" is pathognomonic of pilomatrixoma.