© 2019 American Medical Association. All rights reserved. Importance: Microcystic adnexal carcinoma (MAC) occurs primarily in older adults of white race/ethnicity on sun-exposed skin of the head and neck. There are no formal guiding principles based on expert review of the evidence to assist clinicians in providing the highest-quality care for patients. Objective: To develop recommendations for the care of adults with MAC. Evidence Review: A systematic review of the literature (1990 to June 2018) was performed using MEDLINE, Embase, Web of Science, and the Cochrane Library. The keywords searched were microcystic adnexal carcinoma, sclerosing sweat gland carcinoma, sclerosing sweat duct carcinoma, syringomatous carcinoma, malignant syringoma, sweat gland carcinoma with syringomatous features, locally aggressive adnexal carcinoma, and combined adnexal tumor. A multidisciplinary expert committee critically evaluated the literature to create recommendations for clinical practice. Statistical analysis was used to estimate optimal surgical margins. Findings: In total, 55 studies met our inclusion criteria. The mean age of 1968 patients across the studies was 61.8 years; 54.1% were women. Recommendations were generated for diagnosis, treatment, and follow-up of MAC. There are 5 key findings of the expert committee based on the available evidence: (1) A suspect skin lesion requires a deep biopsy that includes subcutis. (2) MAC confined to the skin is best treated by surgery that examines the surrounding and deep edges of the tissue removed (Mohs micrographic surgery or complete circumferential peripheral and deep margin assessment). (3) Radiotherapy can be considered as an adjuvant for MAC at high risk for recurrence, surgically unresectable tumors, or patients who cannot have surgery for medical reasons. (4) Patients should be seen by a physician familiar with MAC every 6 to 12 months for the first 5 years after treatment. Patient education on photoprotection, periodic skin self-examination, postoperative healing, and the possible normal changes in local sensation (eg, initial hyperalgesia) should be considered. (5) There is limited evidence to guide the treatment of metastasis in MAC due to its rarity. Limitations of our findings are that the medical literature on MAC comprises only retrospective reviews and descriptions of individual patients and there are no controlled studies to guide management. Conclusions and Relevance: The presented clinical practice guidelines provide an outline for the diagnosis and management of MAC. Future efforts using multi-institutional registries may improve our understanding of the natural history of the disease in patients with lymph node or nerve involvement, the role of radiotherapy, and the treatment of metastatic MAC with drug therapy..