Solitary fibrous tumour (SFT) is rarely found in the orbit; it can occur within a wide age range (14–80 years). A case of a 59-year-old man with unilateral exophthalmos is presented. After CT and MRI investigations, the cause was seen to be an orbital mass that, after surgical removal, was diagnosed histologically as a solitary fibrous tumour. In the orbit, the SFT has a histological appearance identical to that of homonymous pleural lesion. It is characterized by alternating hypercellular and hypocellular areas, the collagen bundles having a keloid-type quality. Immunohistochemically, it showed a strong and widespread reactivity for CD68 and CD34. Correct diagnosis of this infrequent neoplasm needs not only clinical observation but also requires radiological examination (CT, MRI) and, above all, histological assessment. Various primary mesenchymal tumours of vascular and fibrohistiocytic type can mimic the symptoms of SFT, thus only the immunohistochemical profile and the ultrastructural features of the lesion allows it to be diagnosed definitively.