Squamous cell carcinoma (SCC) of the nail bed is rare, and it usually mimics a variety of diseases. Thus, a true diagnosis of subungual SCC may be delayed for years. The appearance of a subungual tumor at presentation is often non-diagnostic, and exploratory nail-plate removal with biopsy is recommended. We have experienced four patients with subungual SCC, and they were treated by Mohs micrographic surgery (MMS). In an average follow-up of 13.5 months, there was no recurrence in all cases. However, in one case, amputation was performed due to local periosteal invasion. In cases of subungual SCC without bone involvement, particular virtue of MMS over amputation is that it permits the preservation of both function and cosmesis of the nail unit. Since the maintenance of function is of the utmost priority, MMS can be considered the most appropriate technique, as it enables us to maximize the preservation of normal anatomy of the finger.