We report an aggressively behaving malignant trichogenic tumor arising in a trichoblastoma (TB) with widespread lymphatic and hematogenous metastases in a 55-year-old man with a concomitant B-cell chronic lymphocytic leukemia. The primary tumor had been present and unchanged for as long as 40 years before excision. Typical trichogenic TB with dystrophic calcification and even ossification was still present peripheral to the malignant transformation. The malignant neoplasm consisted of basaloid cells, spindle cells arranged in fascicles and densely packed rounded nests or "cell balls." The metastases consisted of immature basaloid cells and cell balls, and the recurrences became successively more undifferentiated. The residual TB reacted with antibodies to cytokeratin (CK) 6, 8, 14, and 17 and focally to S-100; the malignant primary tumor reacted uniformly with antibodies to vimentin and only focally with antibodies to CK and S-100. The metastatic tumor had lost epidermal CK expression but maintained expression of S-100 in paraffin-embedded tissues. Trichoblastic differentiation was confirmed in frozen tissues with antibodies to hair keratins. No expression of p53 or bcl-2 was identified, but p-glycoprotein (MDR-1 gene related) was expressed by primary and metastatic tumor cells. We believe that this neoplasm is best classified as a trichoblastic carcinoma arising in a TB in association with a B-cell chronic lymphocytic leukemia. This case illustrates that TBs have the potential for malignant transformation and aggressive behavior.