Proliferating trichilemmal tumor is a rare cutaneous neoplasm derived from outer root sheath of the hair follicle. Malignant proliferating trichilemmal tumor (MPTT) invades surrounding tissues or metastasizes with features of cellular pleomorphism and nuclear atypia. Generally, about 90% of cases of the PTTs occur on the scalp. A 58-year-old woman presented with solitary dark brownish colored mass on the left posterior thigh of 6-years’ duration. Ultrasonography showed a 4x4x3 cm sized inflammatory mass in the subcutaneous fat layer with multifocal calcifications. Histologic examination revealed proliferating nests of squamoid cells throughout the dermis with foci of trichilemmal keratinization, infiltrated to adjacent tissue with moderate degree of atypia and pleomorphism. Immunohistochemistry findings were positive for Ki-67, p53, CD34 and calretinin. No evidence of distant metastases was detected from further evaluations of image studies. The patient was diagnosed with MPTT and underwent surgical excision without any evidence of recurrence at 6 months.