Identity testing using DNA, which has been developed and used most often in forensic medicine, has important applications in anatomic and clinical pathology laboratories. These include identification of mixed-up specimens and identification of "floaters" in paraffin blocks or on slides of surgical pathology specimens. Polymerase chain reaction-based identity testing now provides a tool to address these challenging issues of specimen mislabeling, misidentification, and tissue contamination. We examined a case from a 35-year-old man with a laryngeal biopsy specimen that showed a fragment of benign salivary gland tissue and a separate fragment of squamous cell carcinoma. Because the carcinoma diagnosis was unexpected, identity testing on the paraffin-embedded tissue block was performed at the molecular diagnostic laboratory along with testing of the patient's repeat biopsy specimen. The presumed "floater" showing squamous cell carcinoma, and the remaining benign tissue were microdissected using the Pinpoint Slide DNA Isolation System. DNA was extracted and the genetic pattern for each sample was determined using a forensics kit employing short tandem repeats and the amelogenin locus, using multiplex polymerase chain reaction and capillary electrophoresis. The genetic pattern from the squamous cell carcinoma did not match with the benign tissue or the rebiopsy. This result indicates that the fragment with squamous cell carcinoma most likely did not originate from this patient. Resolution of specimen mislabeling or sample mix-ups is essential to prevent serious clinical consequences. In this article, we examine the current status of clinical laboratory medicine identity testing as it applies to surgical pathology, including reviewing the techniques and approaches used, and provide a discussion of clinically relevant pitfalls related to identity testing of anatomic pathology samples. © 2010 Lippincott Williams & Wilkins, Inc.