Malignant sebaceous tumors need to be considered with more than just passing interest by both the clinician and the histopathologist, because one type, the sebaceous gland carcinoma, is capable of metastasizing and causing death. This rare and misunderstood tumor is infrequently diagnosed, and a principal reason for this difficulty is the nonspecific clinical and gross pathologic appearance of the lesion. In addition, there are tumors composed of basal cells, squamous cells, sebaceous cells, and clear cells, which are easily confused with sebaceous gland carcinoma. The purpose of this study was to establish acceptable criteria by which these tumors could be differentiated, and to present the experience at the Mayo Clinic with a group of malignant sebaceous tumors. The possibility of a malignant sebaceous tumor is suggested clinically by the presence of a slow-growing, hard, yellow nodule located on either the face or scalp of a male person. Additional nonspecific aids