A 14-day-old boy presented with a large congenital melanocytic nevus over his left thigh with approximately 17 satellite nevi distributed over the rest of his skin surface. Six weeks later, he developed generalized tonic-clonic seizures and additional satellite nevi became apparent (n > 20). A subsequent brain magnetic resonance imaging demonstrated right temporal T1 hyperintense signal abnormality. At 4 months of age the patient underwent a lumbar puncture that was normal without evidence of melanocytes or tumor. Nevertheless, a few days later he underwent resection of his right medial temporal lesion which demonstrated melanocytosis in the temporal lobe as well as melanocytosis in subependymal areas in other parts of the brain and ventricles, confirming the suspected diagnosis of neurocutaneous melanocytosis. Our case supports previous studies that conclude that the number of satellite nevi is a greater predictor of neurocutaneous melanocytosis than is the location of large congenital melanocytic nevus. In our case, cerebrospinal fluid studies were not reliable even in the face of florid neurocutaneous melanocytosis involving the leptomeninges and ventricles.