Chromosomal analysis of nine benign leiomyomas of the uterus after short-term culture showed karyotypic abnormalities in four cases. All four exhibited multiple chromosome changes, including three cases characterized by complex chromosome rearrangements involving a number of chromosomes. Among others, these rearrangements included a translocation between chromosomes 12 and 14 in one case, a deletion of chromosome 7q in two cases, and both del(7q) and a complex translocation involving chromosomes 12 and 14 in another case. These results confirm the involvement of chromosomes 7, 12, and 14 in leiomyomas and indicate that benign tumors can also be characterized by complex cytogenetic changes.