The opening statement of the historical section of the current version of the DSM is as follows: "The need for a classification of mental disorders has been clear throughout the history of medicine, but there has been little agreement on which disorders should be included and the optimal method for their organization." The authors of the DSM further caution that "for forensic purposes, there are significant risks that diagnostic information will be misused or misunderstood. These dangers arise because of the imperfect fit between the questions of ultimate concern to the law and the information contained in a clinical diagnosis." Despite this caution, however, anecdotal evidence suggests that it is rare for psychiatric or psychological expert testimony to be presented without a DSM diagnosis. A majority of DSM diagnoses rely substantially on an examinee's report of private, internal, and unverifiable experiences. Translating these subjective expressions into a diagnosis adds unjustified credibility to them. Even with a thorough use of collateral sources of information, the clinician must rely on the diagnostic interview. This article argues that as a general rule, forensic mental health professionals should not be permitted to testify in terms that include a psychiatric diagnosis unless required to do so to address the requirements of relevant legal standards. Under such circumstances, experts should always focus on legally relevant behaviors, capacities, and functioning. A diagnosis should only be included in the testimony when it adds information that is reliable, predictive of legally relevant functioning, and not unfairly prejudicial.