Chromosome analysis of 40 cultured uterine leiomyomas revealed the presence of clonal changes in 32.5% of them, confirming the cytogenetic heterogeneity within this type of tumor, mostly referable to a few cytogenetic subgroups. Preferential involvement of 12q14-15 and 14q23-24 bands in reciprocal and complex translocations was most commonly observed. Deletions of chromosome 7 and changes of chromosomes 1, 2, and to a lesser extent, chromosomes 19 and 22 were also found. Constitutional karyotype of patients bearing tumors with karyotypic abnormalities was examined. In one patient, two cells were found with t(12;14)(q14-15;q23-24) translocation and two with del(14)(q13q23-24). The latter rearrangement was also present as a clonal change in the tumor.