Background: A major controversy in the treatment of melanoma is the width of the surgical margin necessary for complete excision. Although surgical margins have decreased in recent years, the current recommendations are mainly based on arbitrary choices, only two of which have been tested in clinical trials.

Objective: Our purpose was to use prospective data, measuring the extent of subclinical melanoma extensions, to develop guidelines for predetermined surgical margins for the excision of cutaneous melanoma.

Methods: A prospectively collected series of 535 patients with 553 primary cutaneous melanomas was studied. All melanomas were excised by means of the fresh tissue technique of Mohs micrographic surgery with frozen section examination of the margin. The surgical margin needed for excision of melanoma was determined by measuring the invisible extensions of tumor around the melanoma. The minimum surgical margin was 6 mm and the total margin was calculated by adding an additional 3 mm for any melanoma requiring a subsequent stage to remove the tumor completely.

Results: Eighty-three percent of melanomas were successfully excised with a 6 mm margin; 9 mm removed 95% of the melanomas; and a 1.2 cm margin was necessary to remove 97% of all melanomas. Margins to remove melanomas on the head, neck, hands, and feet were wider than those on the trunk and extremities. Margins to remove melanomas that were more than 2 to 3 cm in diameter were wider than for smaller melanomas.

Conclusion: Predetermined surgical margins for excision of melanoma or melanoma in situ by standard surgical techniques should include 1 cm of normal-appearing skin for melanomas on the trunk and proximal extremities that are smaller than 2 cm in diameter, or a 1.5 cm margin for tumors larger than 2 cm in diameter. For melanomas on the head, neck, hands, and feet, a minimum surgical margin of 1.5 cm is recommended or a margin of 2.5 cm for melanomas larger than 3 cm in diameter. Mohs micrographic surgery is a useful alternative to standard surgery when more narrow margins are desired, particularly for melanomas on the head, neck, hands, and feet, or melanomas larger than 2.5 cm in diameter, or for melanomas without distinct clinical margins. (J Am Acad Dermatol 1997;37:422-9.)