Management of large congenital melanocytic nevi and neurocutaneous melanocytosis represents a difficult challenge for clinicians, due to the high risk of malignancy in both entities and the difficulty of an early diagnosis of this complication. We report a new case of neurocutaneous melanocytosis (NCM) in association with large congenital melanocytic nevi (LCMN) that illustrates a possible role of positron emission tomography in the work-up of these patients.