Pleomorphic leiomyosarcoma of soft tissue is relatively rare and its cytogenetic and molecular genetic data are scarce. We present a case of pleomorphic leiomyosarcoma arising in the left thigh of a 60-year-old man. Fluorine-18-deoxyglucose positron emission tomography imaging showed a homogenously high uptake within the mass in the proximal left thigh (maximum standardized uptake value, 20.9). Following a core needle biopsy, wide resection of the tumor was performed. Histologically, the tumor was composed of a mixture of spindle cells, polygonal cells and bizarre giant cells forming interlacing bundles and a storiform pattern. Immunohistochemically, the tumor cells were positive for vimentin, smooth muscle actin and desmin. The MIB-1 labeling index was 19.7% in the highest spot. Cytogenetic analysis exhibited a complex karyotype with several numerical and structural alterations, including giant marker and ring chromosomes. Spectral karyotyping demonstrated that giant marker and ring chromosomes were composed of material from the X chromosome. Metaphase-based comparative genomic hybridization analysis showed high-level amplifications of 1q21-q25 and 12q13-q21 and gains of 1p31-p32, 10p11-p13, 17p11 and 19p13. The patient received postoperative adjuvant radiotherapy and doxorubicin-based chemotherapy. No local recurrence or distant metastasis was detected during a follow-up period of 19 months. The clinicopathological, cytogenetic and molecular genetic features of pleomorphic soft tissue leiomyosarcoma are discussed.