BackgroundFibrous dysplasia (FD) is a rare, sporadic, and benign congenital condition in which normal cancellous bone is replaced by fibro-osseous tissue with immature osteogenesis. FD localized in the cranial and facial bones is called craniofacial fibrous dysplasia (CFD). Cystic degeneration in CFD cases is rare; cystic degeneration appearing in both the maxilla and the mandible FD lesion is even rarer. The aim of this article was to report a case of fibrous dysplasia of the mandible and maxilla complicated by nonspecific cystic degeneration.Case presentationA 30-year-old woman presented with a rare case of non-specific cystic degeneration in a mandible and maxilla FD lesion that occurred 11 years after surgery. She was diagnosed with polyostotic CFD and underwent maxillary and mandibular bone contouring. Cyst enucleation under general anesthesia was performed in the mandibular region due to pain and discomfort.ConclusionsIn cases involving non-aggressive and non-invasive FD cystic degeneration in focal areas, conservative treatment is recommended. However, if cystic degeneration of FD develops rapidly and causes discomfort, pain, or dysfunction, surgical treatment should be considered.