Thirty samples from 19 patients with synovial sarcoma were analyzed cytogenetically after short-term culturing. Thirteen samples were from primary tumors, 11 from local recurrences, and six from distant metastases. All samples showed the characteristic aberration t(X;18)(p11;q11) or variants thereof; 23 samples had additional numerical and/or structural changes. Including the present cases, chromosome aberrations have been reported in 74 synovial sarcomas, 50 of which have had secondary aberrations in addition to t(X;18). No secondary structural aberration was recurrent. The most common numerical changes were +7, +8, +12 (10 cases each), -3, +9, +21 (7 cases each), +2, -14, -17 (6 cases each), +4, -11, +15, and -22 (5 cases each). Unbalanced stuctural aberrations led to loss of 3p and 17p in six cases, each with loss of bands 3p21 and 17p13, respectively, in common. Most monosomies and trisomies seemed to occur at similar frequencies in primary, recurrent, and metastatic tumors. The only exceptions were +2, which was never seen in a primary tumor, and +8, which was never found in any metastatic lesion.