Summary.We report a case of oral squamous cell carcinoma (SCC) originating in the buccal mucosa of an 18-year-old female patient with chronic graft-versus-host disease (GVHD) 9 years after HLA-identical sibling bone marrow transplantation (BMT) for Fanconi anaemia (FA). The case highlights the problems of malignant change in FA and also the increased risk of second malignancy after BMT. The literature is reviewed with regard to previous cases and the possible aetiology of tumour formation. A high index of suspicion to any epithelial lesion in FA is appropriate so that early diagnosis may lead to improved prognosis. Keywords:Fanconi anaemia, squamous cell carcinoma, bone marrow transplantation, immunosuppression, microvascular free flap.An 8-year-old girl presented with mild hypoplastic anaemia and was found to have FA after a positive mitomycin C stress test on peripheral blood lymphocytes. Her parents were not related and there was no family history of FA. She underwent BMT the following year with marrow donated by her HLAidentical sister who did not have FA. Pre-transplant conditioning consisted of low-dose cyclophosphamide (5 mg/kg/d × 4 d) and total body irradiation (TBI) 600 cGy, with oropharyngeal shielding. Severe acute GVHD of skin and gut was followed by chronic cutaneous and hepatic GVHD with an associated sicca syndrome. This was still being treated with cyclosporin A and azathioprine at age 18 years when the patient presented with a swollen right cheek and a large painful ulcer of the buccal mucosa. Biopsy confirmed a moderately well differentiated SCC. There was no clinical lymphadenopathy and nothing to suggest local or systemic dissemination. Full blood count was Hb 13 . 9 g/dl, WBC 7 . 1 × 10 9 /l, neutrophils 4 . 3 × 10 9 /l and platelets elevated at 436 × 10 9 /l. Chest X-ray was normal. A decision was made to treat surgically; the size and position of the tumour suggested that it was locally resectable, and it was considered desirable to avoid further radiotherapy or chemotherapy. The lesion of the right buccal mucosa was resected with a full thickness excision which included the right commissure and part of the maxillary alveolus with attached molar and premolar teeth. An ipsilateral supraomohyoid neck dissection was carried out. The intra-oral defect was reconstructed with a left radial forearm free flap. A full thickness abdominal skin graft was used to cover the arm donor site, and primary closure was achieved on the cheek. All the grafts remained viable and healed well, and the patient was discharged on the 15th post-operative day.Histopathological examination of the operative specimen showed a moderately differentiated invasive squamous cell carcinoma with perineural and vascular spread (Fig 1). The absence of lymphocytic response to tumour in the surrounding tissues was particularly striking. Histological features of chronic GVHD were evident in the buccal mucosa, though less than on the preoperative biopsy specimen. Two cervical lymph nodes contained metastatic deposits.One month after...