Leiomyosarcomas of soft tissues are an aggressive group of tumors with a high incidence of recurrence. Little is known about the molecular genetic changes associated with clinical outcome. Therefore, we studied 28 leiomyosarcoma samples of similar grade using comparative genomic hybridization and DNA flow cytometry and identified a difference in survival time associated with ploidy status and the number of chromosomal aberrations. The average survival time was shown to decrease with increase in chromosomal aberrations identified using comparative genomic hybridization. The average survival time was shorter in the near-tetraploid group than in the diploid and triploid group. Gain of 5p14-pter was significantly more common in near-tetraploid tumors. The survival time of patients with near-tetraploidy together with gain of 5p14-pter was reduced, and 50% died within the 1st year. Furthermore, loss of 13q14-q21 was significantly more frequent in the <5-year than in the >5-year survival group (P =.01). These results suggest that 13q14-q21 loss and 5p14-pter gain at diagnosis could be used to identify patients with leiomyosarcoma who are likely to have a shorter survival time and who might benefit from early treatment intensification.