Optical coherence tomography (OCT) has potential as a modality for in vivo imaging of non-melanoma skin cancer (NMSC). By allowing identification of sub-surface margins of NMSC lesions, the use of OCT could improve the rate of complete excision and reduce the average number of stages during Mohs micrographic surgery (MMS). The objective of this study was to use OCT to delineate the apparent sub-surface margins of NMSC lesions prior to their excision by MMS. Lesions were scanned with reference to a physical marker on the skin, and the apparent margins were then identified from the OCT images and marked on the skin. Photographs of these margins and the Mohs defect were correlated and compared. OCT appears capable of visualizing the transition from lesional to normal tissue. In this case study, margins marked by use of the OCT system before surgery exhibit excellent correlation with the MMS defect. OCT offers the promise of better outcomes by enabling accurate margin mapping of NMSC in advance of MMS. Priorities now are to demonstrate this capability in a larger study, and to understand clearly indications and contraindications for use.