Positive results for the use of anabolic steroids in a urine sample provided by an athlete were challenged by allegations of urine tampering during the doping control procedures. The chain of custody in this case was reviewed and no flaws were discovered. The athlete demanded DNA testing to prove that the steroid-tainted urine was not obtained from her. DNA sequencing subsequently indicated that the steroid-tainted urine could not be matched to the DNA obtained from the athlete’s blood. However, the urine sample contained mitochondrial DNA with nucleotide sequences spanning the hyper variable regions HV1 and HV2 that were identical to those found in the athlete’s blood. In this case, it was not possible to exclude the possibility that a sibling or a maternal relative of the athlete could have provided the urine obtained for doping control and DNA analysis. The case indicated possible tampering by the athlete, particularly since there was no proof of a chain of custody flaw that would allow for urine substitution after collection.