Maintaining patient identity throughout laboratory processing is critical for any diagnostic pathology laboratory. It has also been listed as a main National Patient Safety Goal for the Joint Commission Laboratory Goals. Most pathology facilities have excellent quality assurance programs and initiatives that include multiple checkpoints to ensure that specimen identity is carefully maintained. Even in the best laboratory operations, however, the potential for specimen mix-up, cross contamination, floaters, or carry-over artifacts cannot be eliminated completely. The work-up and analysis of these cases can be challenging to the pathologist for a number of reasons, including the fact that there is no standardized approach. This review discusses a standardized approach that includes clinical correlation, laboratory correlation, and laboratory analysis, potentially including a molecular DNA fingerprinting analysis. The methods and techniques behind DNA fingerprinting for tissue and sample identity are also discussed in detail.