Giant congenital melanocytic nevi (GCMN) may be associated with a variety of malformations. Recently, atrophy of the underlying extremity was reported for the first time. We observed two patients with GCMN on the extremities with marked atrophy of the underlying tissue without functional impairment. According to the definition of hamartoma, it seems possible that one component of tissue has decreased. Dermatologists treating patients with such nevi in the first weeks of life with dermabrasion, laser, or curettage need to know that the natural course of GCMN may lead to atrophy and that this does not necessarily result from the treatment regimen.