We report the first cytogenetic analysis of a leiomyosarcoma of the sinonasal tract, a rare neoplasm. Karyotypic analysis showed near-triploid and near-tetraploid modal chromosome numbers with extensive structural and numerical aberrations. Three consistent structural changes, including i(6p), der(10)ins(10;1)(q26;q23q44), and der(12)t(1;12)(q11;q24) were observed in most cells. A der(11)t(11;?)(p15;?) was observed in 14 of 20 cells. Clonal structural rearrangements, including i(1q), del(2)(q37), der(3)t(3;?)(p25;?), del(4)(q31), del(7)(q32), der(12)t(12;?)(p12;?), der(15), del(21)(q22), and der(X) were each observed in a few cells. Numerical changes, including trisomies for chromosomes 2-5, 7, 9, 11, 15, 17, 18, and 20 and monosomies 10 and 12 were observed. Comparison of our findings to those of leiomyosarcomas at different sites showed trisomies 7 and 20 and rearrangements of 11p12-p15 and 21q22.