Background: Microcystic adnexal carcinoma (MAC) is a malignant appendageal tumor first described in 1982. It can be clinically and histologically confused with other malignant and benign cutaneous neoplasms, leading to inadequate initial treatment. This neoplasm is locally aggressive and deeply infiltrating, characterized by high morbidity and frequent recurrence. Mohs micrographic surgery has been used to conserve tissue and improve the likelihood for cure. Objective: We report our experience using Mohs micrographic surgery for the treatment of MAC and compare with earlier reports in the literature. In addition, we review the epidemiology, clinical and histologic characteristics, and optimal treatment of this rare neoplasm. We also describe a 15-year-old white male patient with MAC on the scalp occurring only 7 years after radiation exposure. Methods: The medical records of 11 patients with MAC who were treated by Mohs micrographic surgery were reviewed at both departments, and follow-up data were obtained. Results: In all patients treated with Mohs micrographic surgery, there were no recurrences after a mean follow-up of 5 years. Conclusion: Mohs technique enables the detection of clinically unrecognizable tumor spread and perineural invasion often encountered with MAC. Aggressive initial treatment by microscopically controlled excision appears to offer the greatest likelihood of cure for this neoplasm, while providing conservation of normal tissue. In addition, we describe the second youngest patient with MAC and readdress the issue of previous radiotherapy as an important predisposing factor. (J Am Acad Dermatol 1999;41:225-31.)