We report a case of giant congenital melanocytic nevi (GCMN) at risk of developing neurocutaneous melanosis (NCM) with age-related changes observable on MRI of the brain. However, although the usefulness of MR imaging in NCM is well known, age-related changes on MRI have rarely been reported. The prevalence of positive MRI findings and prognosis in GCMN accompanied by epilepsy and/or mental retardation awaits clarification. This case report may suggest the importance of serial brain MRI in cases of GCMN in assessing the risk of NCM.