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Mohs micrographic surgery is a highly effective, tissue-conserving method for removing certain cutaneous neoplasms. Horizontal Mohs tissue sectioning permits complete histologic evaluation of the true surgical margin, but does not aim to evaluate the overall morphology of the tumor. Mohs surgery is designed primarily to answer the question “Is it all out?” as opposed to “What is it?” A preoperative biopsy is relied on, in most cases, to provide an accurate diagnosis. The histology from this biopsy might be the only view of the tumor if the first Mohs stage is clear. However, histopathologic review of small biopsies may sometimes give incomplete information about the entirety of the tumor.To illustrate the potential utility of adjunctive histopathologic examination of some tumors treated by Mohs surgery.We present four cases to illustrate situations where pre-Mohs biopsy provided incomplete information. The limitations of these biopsies was clarified after the tumor was visualized on a positive first Mohs layer and/or when the tissue was subsequently sectioned vertically.Cases of tumors where preoperative biopsies gave incomplete information are presented: sebaceous carcinoma versus basal cell carcinoma (BCC), invasive versus in situ squamous cell carcinoma (SCC), and SCC versus keratoacanthoma.The Mohs technique allows histologic examination of the complete surgical margin around cutaneous neoplasms, optimizing tissue sparing and resulting in superior cure rates. However, in rare cases additional evaluation of the tissue by vertical sectioning can provide important adjunctive histopathologic information that can effect ultimate patient management.