Solitary fibrous tumors are uncommon spindle cell neoplasms originally thought to be restricted to the pleura. We describe a 62-year-old woman who presented with stridor and an anterior mediastinal mass. At thoracotomy, a 10.5 x 6.5 x 5.5 cm, circumscribed, firm mediastinal mass demonstrated no direct cardiac or pulmonary involvement. The tumor consisted of spindle cells organized in a patternless pattern with collagenous stroma and hemangiopericytoma-like vessels. Spindle cells were immunoreactive for CD34, CD99, desmin, vimentin and bcl-2 protein and a diagnosis of mediastinal solitary fibrous tumor was confirmed. The differential diagnosis of mediastinal solitary fibrous tumors is extensive and includes spindle cell thymoma, sarcomatoid carcinoma, malignant mesothelioma, inflammatory myofibroblastic tumor, peripheral nerve sheath tumors and various sarcomas. Despite their rarity in the mediastinum, solitary fibrous tumors can be recognized by their classic patternless morphology and immunophenotypic pattern. Their accurate classification is important, as solitary fibrous tumors are intermediate (rarely metastasizing) neoplasms that require complete surgical excision and long-term clinical follow-up for optimum therapy.