Solitary fibrous tumours are rare spindle-cell neoplasms that usually arise from visceral and parietal pleura and peritoneum and are likely of either mesothelial cell origin or fibroblast/primitive mesenchymal cell origin.1 They are typically found in the chest and occasionally the abdominal cavity but have been reported in the parotid gland, pericardium, ovary, liver, intestine, lung, orbit, upper respiratory tract, bladder and periosteum.2 Solitary fibrous tumours involving the diaphragm arising from overlying pleura or underlying peritoneum have been occasionally described but never with such intimate involvement. A 32-year-old female smoker presented with clinical features typical for gallstones. An ultrasound of her biliary system confirmed cholelithiasis but also noted a large heterogeneous solid hypoechoic mass medial to the spleen in the left upper quadrant. Beyond issues with symptoms related to gallstones, she denied any other problems including breathlessness, atypical chest pain or referred pain. She had no night sweats or weight loss, and clinical examination was unremarkable. A chest computerized tomography (CT) demonstrated a large mass in intimate contact with the left hemidiaphragm (Fig. 1a,b). Following standard general anaesthesia and single lung ventilation, a left video-assisted thoracoscopic assessment showed the mass appearing to be within the diaphragm or pushing up from the abdomen. A laparoscopy was performed, which confirmed the mass was within the diaphragm itself (Fig. 2) and completely separate form underlying abdominal viscera. Following left thoracotomy, a full thickness excision of the hemidiaphragm with the tumour contained within its leaves was completed. The hemidiaphragm was reconstructed using Gore-Tex (Flagstaff, AZ, USA). Chest CT demonstrating the heterogeneous mass intimate to the left hemidiaphragm in transverse (a) and coronal (b) sections (white arrows). Laparoscopic view of the tumour protruding into the abdominal cavity. The patient went on to make an uneventful recovery, and following discharge at one-year follow-up, was fully recovered with a chest CT showing no evidence of recurrence. Tumour inspection found grossly normal diaphragmatic tissue covering both sides of the specimen. Immunoperoxidase stains demonstrated strong diffuse cytoplasmic positivity for CD34 as well as vimentin, Bcl-2 and S100, but a lack of strong cytokeratin positivity. The morphologic and immunophenotypic features were those of a solitary fibrous tumour. Solitary fibrous tumours can arise at any age in either sex but typically presents after the fourth decade as a slow growing painless well-circumscribed mass.1,2 Up to 20% of tumours exhibit malignant features including ‘paraneoplastic-like syndromes’ such as hypertrophic pulmonary osteoarthopathy, hypoglycaemia and clubbing3 as well as local recurrence and distant metastasis. Histologically, malignancy is suggested by the presence of pleomorphic cells with atypical nuclei, high mitotic rate and necrosis. The unifying characteristic of solitary fibrous tumours is positive staining for CD-34, resulting from the spindle cells. Positive immunostaining for Bcl-2 and CD99 is also observed, but their presence is not uniform and positivity is often weak.4 Surgical resection of the tumour is the treatment of choice, with any associated paraneoplastic syndromes typically resolving following complete excision.3,4 Local recurrence is possible if incompletely excised, and malignant transformation has been reported.2 The use of neoadjuvant chemotherapy along with post-operative radiation therapy in cases of large tumours with positive surgical margins after resection has been described.5 Long-term clinical follow-up is recommended, particularly if the histological evaluation suggests malignancy.