Primary synovial sarcoma of the thorax is rare. Origin of thoracic synovial sarcoma in the pleura or lung was first described only 7 years ago. Radiologic characteristics of this disease have not yet been studied in a formal series. The authors sought to define the radiologic features of primary thoracic synovial sarcoma and to correlate the findings with clinical and pathologic features. They examined clinical, radiologic, and pathologic features of five patients with primary synovial sarcoma of the chest. Radiologic evaluation included conventional radiographs, computed tomographic scans, and magnetic resonance images of the chest. Patients included three men and two women who ranged in age from 28 to 40 years. Primary tumors involved the chest wall (n = 2), lung (n = 1), or both (n = 2). Chest pain was the most common presenting symptom. Although conventional radiographs often showed the lesions to be ill defined, computed tomographic scans showed well-defined masses in every case. Heterogeneous enhancement and an absence of calcification were also seen. Pathologic evaluation demonstrated synovial sarcoma with equal distribution between the monophasic and biphasic variants. The chromosomal translocation X;18 was demonstrated in four of four cases tested. All patients were treated by resection. Recurrence was demonstrated radiologically in four patients at 2 to 14 months. All patients were alive at 9 to 58 months of follow-up. The authors conclude that primary synovial sarcoma of the chest occurs in young adults, most commonly presenting with chest pain. It is characterized radiologically by a heterogeneously enhancing well-defined mass without calcifications.