The thickness of melanoma (Breslow method) is the single most important prognostic indicator. It is measured using an ocular micrometer on excisional biopsy specimens. Other types of biopsy specimens (shave, punch, wedge) are not suitable for measuring Breslow depth. The measurement is taken from the most superficial part of the granular cell layer of the epidermis to the deepest point of tumor invasion. If ulceration is present, the measurement is taken from the base of the ulcer. Polypoid tumors are measured through their thickest region. The biological significance of tumor invasion of adnexal structures is unknown. If the tumor extends deeply along the adnexal structures, this information is documented along with the Breslow thickness. Although depth of invasion is a continuous variable, for staging purposes, the AJCC guidelines use cut offs of 1mm, 2mm, and 4mm. The case shown here had a Breslow thickness of 1 mm.