Müllerian adenosarcoma (MA) is an uncommon biphasic neoplasm of the female genital tract, composed of malignant stroma and benign epithelium. Little is known about the molecular and cytogenetic aberrations in MA pathogenesis, including those with progression to sarcomatous overgrowth (SO). Herein, we report all cases of MA in which karyotyping was attempted at our institution. Twenty-one samples from 20 subjects consisted of 15 primary (7 without SO, 8 with SO) and 6 metastatic MA, were cytogenetically investigated in our institution. Karyotypes were successfully obtained in 14/21 (67%) cases and 9 (45%) had cytogenetic aberrations. Two (1 MA with SO and 1 metastatic MA) were markedly complex, displaying extreme aneuploidy with numerous rearrangements. Seven (2 MA without SO, 3 MA with SO, and 2 metastatic MA) demonstrated noncomplex clonal aberrations, of which 5 (71%) included an abnormality involving chromosome 8. Two tumors had rearrangements at 8q13 and another 3 tumors had extra copies of chromosome 8. In 5 cases, a normal karyotype (46,XX) was obtained (2 MA without SO, 2 MA with SO, and 1 metastatic MA). Further study is warranted to explore the genetic mechanism by which chromosome abnormalities, particularly those at 8q13, contribute to MA tumorigenesis.