Based upon the experience of 256 cases of synovial sarcoma (SS), the present review analyzes structural, biological and molecular pathology of this poorly known sarcoma. The histology displays a multiphenotype with two major components: biphasic and monophasic SS. In addition, a number of variants have been described: undifferentiated Ewing's like, myoxid and predominantly epithelial (monophasic epithelial sarcoma). Microcalcifications and squamous metaplasia are often seen in the tumor. Immunohistochemistry with EMA and cytokeratin in the epithelial or epithelioid component is diagnostic for SS together with vimentin positivity in the spindle cells. Several other epitopes are also expressed (CD99, CD56, C-MET, HGF/SF, CD44). The ultrastructure confirms the variegated pattern of the neoplasm demonstrating the epithelial component and the epithelioid or spindle cell type closely associated with each other. Transition of epithelial cells to epithelioid and spindle-like mesenchymal component is seen. Nude-mice xenografts and cell lines after in vitro culture confirm heterogeneity of this sarcoma. Molecular histology of the SS has provided high utility not only for their differential diagnosis due to a specific chromosomal translocation: t(X;18)(p11.2;q11.2) but also after cloning these breakpoints resulting in the fusion of two genes: SYT at 18q11 and SSX at Xp11. Further observations have lead to distinguish the existence of two related genes: SSX1 and SSX2, that provide a highly specific and sensitive diagnostic marker for SS. Moreover, clinical correlations have demonstrated that SYT-SSX1 leads to a poor clinical outcome while the fusion SYT-SSX2 provides survival advantages to the patients.