The metaplastic synovial cyst (synovial metaplasia of the skin) is a recently described intradermal cyst lined by a membrane that resembles hyperplastic synovium. All of the reported cases thus far have occurred in adults after surgical incision. A case of metaplastic synovial cyst after partial excision of nevus sebaceus in a 7-year-old girl is herein reported. Pathogenesis and light-microscopic and immunohistochemical features of this case are discussed.