Changes in the acceptance of hair test results in the United States courts have resulted from two factors: the rapidly evolving scientific understanding of hair test data; and modification of the admissibility standards for forensic evidence in United States courts. The scientific, forensic, and ethical aspects of drug testing in hair impact the acceptance of hair test results. Our knowledge and experience with this new analytical technology have been developing rapidly, although there are many unanswered questions that influence acceptance of data. A consequence of the recent U.S. Supreme Court decision to have the Federal Rules of Evidence take precedence over the Frye standard in the admissibility of scientific evidence has enabled judges to determine if evidence will assist in obtaining a fuller understanding of a given case. A summation of the scientific, forensic, and ethical aspects of judicial acceptance of hair test results may be: If hair test results are positive, have we proven beyond a reasonable doubt and/or demonstrated that the preponderance of evidence supports a finding of drug use? In general, recent court decisions indicate that hair test results provide information that the courts should consider. However, unresolved scientific, forensic, and ethical issues may have a greater effect on the weight applied to hair test evidence rather than its admissibility in future court proceedings.