Neurocutaneous melanocytosis (NCM) is a rare congenital neurological disorder characterized by abnormal aggregations of nevomelanocytes within the central nervous system (leptomeningeal melanocytosis) associated with large or giant congenital melanocytic nevi (CMN). NCM can be asymptomatic or present as variably severe and progressive neurological impairment, sometimes resulting in death. The disease is neurocutaneous melanocytosis (MONDO_0009578). Also known as: NCM, neurocutaneous melanosis, neurocutaneous melanosis, somatic.