Cytogenetic analysis was performed after short-term tissue culture of two recurrent synovial sarcomas. The tumors were classified on the basis of morphology, location, and immunohistochemistry. In a poorly differentiated tumor, the karyotype 49,XY, +7, +8, +19,t(5:18) (q11.2;q11.2), and in a biphasic tumor two clonal cell lines with common translocations t(X;18)(p11.2;q11.2) and t(12;17)(p11.2;q11.2) were present. In the predominant cell line several other structural aberrations including t(1;12)(q21;q24.3), t(3;18)(p23;q21), and 17p+ were found. A comparison of our results with previously published studies suggests that in addition to t(X;18), translocations of chromosome 18 with other chromosomes may represent a consistent feature of chromosomal changes in synovial sarcoma.