Basal cell carcinoma recurring after radiotherapy: a unique, difficult treatment subclass of recurrent basal cell carcinoma. Twenty-seven basal cell carcinomas (BCCs) recurring following radiation therapy alone or in addition to other treatment modalities were treated with Mohs micrographic surgery (MMS) from 1983 to 1989. Mean tumor size was 2.1 cm. Of the tumors, 70.4% arose in the mid-face region, 55.6% had undergone multiple previous treatment modalities. The present recurrence rate is 7.4% (mean follow-up: 25 months). Basal cell carcinoma recurring following radiotherapy deserves special subclassification among recurrent BCC. It is very difficult to eradicate, with high recurrence rates following standard surgical excision or further radiotherapy. Tumors are usually large, aggressive, and invasive. Most arise in the cosmetically crucial mid-face region, where extension into subcutaneous tissue planes is common. Mohs surgery, with its inherent abilities to examine all margins, map tumor extension, and conserve tissue, is uniquely suited to treatment of these difficult tumors. 