The need to accurately identify tissue of an individual can arise in a variety of settings including mislabelled slides or sample carryover. Reported rates of carryover range from 0.6% to 2.9% of slides depending on the methods of evaluation. Carryover becomes particularity clinically important when malignant tissue is found in an otherwise benign sample. The suspicion of malignancy causes immense psychological stress to the patient and results in additional management costs due to the additional investigations required to rule out malignancy. Proving a negative can be difficult and many cases result in lifelong follow-up for the patient. Molecular techniques such as PCR amplification of simple tandem repeat (STR) sequences can be used to identify tissue and hence its provenance. At University College London Hospital, STR PCR analysis has been used since 2003. Here the authors report their experience with regard to the clinical scenarios, the technique used and the outcomes.