Mohs micrographic surgery, more commonly referred to as Mohs surgery, is a surgical technique that uses histologically prepared frozen tissue sections, which are interpreted by the surgeon who actually performed the surgery, to evaluate the surgical margins of excisions performed to remove skin cancers. The surgeon is trained both in dermatological surgery and in interpreting the pathology of the removed specimens. By using microscopic control and horizontal excisions and sectioning of cutaneous neoplasms, this procedure is able to maximally conserve the greatest amount of normal tissue and at the same time provide the highest cure rate possible. This is true even for anatomic locations at high risk of recurrence such as the central face, nose, eyelids, and the ears. It is also very good for recurrent tumors that have failed to respond to previous treatment and for sclerosing or morpheaform types of basal cell carcinomas.

Using this technique the surgeon marks the tissue before removing the specimen from the patient. After the specimen is removed it is again marked with stains based on the pre-surgical markings. The tissue is then processed using a freezing microtome and then is examined by the surgeon after this process is complete. Once the pathology is evaluated it can be determined if the entire tumor has been removed. If any surgical margins are positive for residual tumor the surgeon can know exactly where it is located based on the pre-surgical markings and can proceed with another stage of surgery just where the margins are positive leaving the remaining margins intact. This ensures the tumor is removed completely with minimal tissue loss along with minimal defect formation after the tumor has been cleared.