OBJECTIVE To report a case of a malignant proliferating trichilemmal tumor (PTT) in the right postauricular region, and to describe the clinical and histopathologic findings.METHODS Interventional case report and literature review.RESULTS A 46-year-old woman presented with a 15-year history of a nodule of 30×30×10 mm in diameter in the right postauricular region. It was diagnosed as a sebaceous cyst. A local mass excision was performed. Histopathologic examination revealed proliferation of the outer hair sheath epithelium with multiple central areas of trichilemmal keratinization. The presence of marked cellular atypia and frequent mitoses indicated a malignant transformation. A second operation employing an enlarged excision was conducted followed by a histopathologic examination showing that there was no malignant tumor remaining. Two weeks after the second operation, 50 cGy of regional prophylactic radiotherapy was applied. The patient was well after 26 months of follow-up and neither recurrences nor metastases were observed.CONCLUSION Malignant PTT is a rare skin neoplasm, with its diagnosis depending on a histopathologic examination. An extend excision is the main treatment after diagnosis.