The clinicopathologic and immunohistochemical features of one orbital and nine extraorbital soft tissue lesions, the morphology of which overlaps with giant cell angiofibroma and solitary fibrous tumor, are presented. There were 3 male and 7 female patients. Age at diagnosis ranged from 18 to 81 years (median: 45 yrs). Development of a mass was the main presenting symptom. For two patients, the lesion had been evident for several years before excision. Extraorbital tumors were located in the head and neck area (3), back (3), retroperitoneum (1), hip (1), and vulva (1). Tumor size ranged from 1.3 cm to 11 cm (median: 4.5 cm). The lesions presented grossly as well-demarcated, unencapsulated soft tissue masses. Histologically, they were characterized by the presence of alternating cellular and sclerosing areas, keloidal collagen deposition, round- to staghorn-shaped, thick-walled vessels and multinucleated giant stromal cells often lining pseudovascular spaces. Cellular areas were composed of non-atypical spindle to round cells set in a variably collagenous background. Mitotic activity ranged from 1 to 3 mitoses/10 high-power fields. Immunohistochemical studies showed positive staining of the spindle/round cells and multinucleated stromal cells invariably for vimentin, CD34, CD99, and mostly for bcl-2 but negative for muscle specific actin, desmin, CD31, CD117 (c-kit), and inhibin. Occasionally, focal reactivity was observed for smooth muscle actin, S-100 protein, epithelial membrane antigen, and keratin. Treatment consisted of simple tumorectomy in eight patients and wide excision in two. Follow-up information for eight patients (range: 7-32 mos; median: 14 mos), including four with microscopically positive surgical margins, showed no recurrence. These lesions share the clinical, pathologic, and immunohistochemical features of giant cell angiofibroma and solitary fibrous tumor, supporting the view that these tumors are closely related. In addition, it shows that giant cell angiofibroma occurs equally in both sexes and has a wider distribution than initially thought, developing even more often in extraorbital locations than in the orbit