We report the case of a 57-year-old immunocompromised man with a pilomatrix carcinoma in his left forearm. Pilomatrix carcinoma is the rare malignant counterpart of pilomatrixoma. It has a potential for local recurrence and can metastasise to distant sites. We discuss the differential diagnosis of this rare tumour, and the difficulty in distinguishing this lesion from an atypical proliferating pilomatrixoma. Ultrastructural features of pilomatrix carcinoma are also discussed.