Synovial sarcoma is the fourth most common type of soft-tissue sarcoma, accounting about 10% of all primary soft-tissue malignancies worldwide. Synovial sarcoma most often affects the extremities, particularly the knee in the popliteal fossa, of adolescents and young adults (15–40 years of age). Despite its name, the lesion does not commonly arise in an intraarticular location but usually occurs near joints. Although radiographic features of these tumors are not pathognomonic, findings of a soft-tissue mass, particularly if calcified (30%), near but not in a joint of a young patient, are very suggestive of the diagnosis. Two features associated with synovial sarcoma that may lead to an initial mistaken diagnosis of a benign indolent process are slow growth (average time to diagnosis, 2–4 years) and small size (< 5 cm at initial presentation). Synovial sarcoma is an intermediate- to high-grade lesion, and, despite initial aggressive wide surgical resection, local recurrence and metastatic disease are common and prognosis is guarded. Understanding and recognizing the spectrum of appearances of synovial sarcoma are important for optimal patient management.