More than 40% of basal cell carcinomas referred for removal of the residual tumor were BCC-MH. An unsuspected aggressive pathologic pattern of growth may not be detected after a superficial biopsy. Subsequently, the cancer may recur if the initial treatment for the diagnosed nonaggressive tumor subtype is inadequate for the undiscovered aggressive carcinoma. Mohs micrographic surgery is recommended for BCC-MH treatment.