We describe an 8-year-old boy with Rubinstein-Taybi syndrome, a multiple congenital anomaly/mental retardation syndrome characterized by broad thumbs and great toes, peculiar facies, and mental retardation caused by mutations in the transcriptional coactivator CREB binding protein (CBP). He had on his right side yellowish papular lesions organized in narrow bands according to Blaschko lines, later confirmed by histology as an epidermal nevus. Epidermal nevus syndrome has been ruled out because the patient failed to meet the criteria for inclusion under this designation. This association may be coincidental.