The light microscopy and ultrastructural features of two maxillofacial synovial sarcomas are presented. By light microscopy, one of the tumors revealed the typical biphasic pattern while the other was predominantly fibrosarcomalous. Ultrastructurally. both cases revealed a biphasic pattern, Epithelial-like cells displayed abundant mitochondria, Golgi profiles, electron-dense bodies, cytolysosomes, and thin filaments. Stromal cells were spindle-shaped and provided with smaller cytoplasm and scant organelles, mainly consisting of profiles of rough endoplasmic reticulum, mitochondria, and free ribosomes. Pseudoglandular spaces lined by cuboidal to flattened epithelial-like cells with apical microvilli were numerous. Basal lamina and intercellular junctions were prominent in one case, but sparse in the other. The most undifferentiated tumor revealed many intercellular clefts containing filopodia among the epithelial-like cells: occasional inlraeytoplasmic lumina were also present. These findings are somewhat similar to those reported in normal and nonneoplastic diseases of the synovium. However, the location of the tumors in areas normally devoid of synovium suggests once more that they might arise from nonspecialized primitive mesenchyme.