The clinical, histologic, and histochemical findings in three cases of a dermal sweat duct tumor are described. Histologically, the tumor presents as solid or cystic masses of basaloid cells in the dermis, intimately related to the dermal sweat duct. The epidermis shows occasional poroma-like involvement related to the underlying tumor masses. Histochemically, the tumor masses show moderate amounts of glycogen and massive phosphorylase activity, indicating their relationship to the sweat duct. Histologically and histochemically, the tumors can be differentiated from basal cell epithelioma, eccrine poroma, and hidradenoma.