Benign uterine leiomyomata are the most common tumors in women of reproductive age. One recurring chromosomal aberration in uterine leiomyomata is rearrangement of 10q22. Chromosome 10 breakpoints were mapped by fluorescence in situ hybridization to intervals ranging from 8.9 to 72.1 kb within the third intron of MORF (monocytic leukemia zinc finger protein-related factor or MYST4) in four uterine leiomyomata tested. Additional Southern hybridization experiments confirmed that the breakpoint lies within the third intron and narrowed the interval to 2.1 kb in one uterine leiomyomata. MORF is a member of the MYST family of histone acetyltransferase and previously has been found rearranged in some types of acute myeloid leukemia (AML). This is the first instance in which disruption of a histone acetyltransferase has been reported in another tumor type. The breakpoints in uterine leiomyomata would fall in the NH₂-terminal portion of the protein between a conserved domain found in histones H1 and H5 and the PHD zinc fingers, the CH2CH zinc finger, or the CoA binding site, which is distinct from the breakpoints reported in AML. Mapping of the 17q21 breakpoint by fluorescence in situ hybridization within a specific region in three tumors revealed several positional candidates including GCN5L2, a gene with histone acetyltransferase activity similar to those fused to MORF in AML. Of note, two of three uterine leiomyomata were of the cellular subtype. Involvement of MORF in four uterine leiomyomata with chromosomal rearrangements involving 10q22 and 17q21 suggests a role for this histone acetyltransferase and altered chromatin regulation in uterine mesenchymal neoplasia.