BACKGROUND Complete surgical excision of melanoma in situ (MIS) is curative. A 5-mm margin is often taken as the standard primary excision margin despite increasing evidence that this is frequently inadequate for tumor clearance. OBJECTIVE To calculate the proportion of patients requiring >5 mm margin for clearance and to investigate any patient/lesion characteristics necessitating larger margins. MATERIALS AND METHODS Three hundred forty-Three primary MIS cases on the head and neck treated in the authors' department by Mohs micrographic surgery (MMS) over a 65-month period were retrospectively analyzed. Records were made of patient and lesion characteristics, and the total surgical margin for clearance calculated. RESULTS Sixty-five percent were cleared by a 5-mm margin; for a 97% clearance rate, 15 mm was necessary. The increased clearance with additional margin was significant (p < .0001). Patient age, lesion site, and preoperative size did not predict margin. CONCLUSION These results verify that MIS on the head and neck can spread significantly beyond the clinical margin and demonstrate the importance of confirming clearance histologically before closure procedures. Mohs micrographic surgery has the advantage of total margin evaluation and where available it may be reasonable to start with a 5-mm margin. Where MMS is not a treatment option, the authors would advocate larger excision margins of ≥10 mm.
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