A psychiatric evaluation of the complaining witness in a criminal proceeding may be necessary to permit informed deliberation by the jury. In cases where doubt exists about whether the complainant may be psychiatrically impaired, information about the mental state of the complainant is germane and should be made fully clear to the jury. The danger of such a use of psychiatry is that it may be overused and misused to harass and stigmatize complaining witnesses if not managed judiciously and vigilantly; e.g., a New York court has ruled that although the right to psychiatric testimony clearly exists, the defendant must make a clear showing that it is warranted in view of the infringement on the complainant's right to privacy. Although the competency of a juror to render a judgement in a case is recognized as a possible impediment to justice being done, there is a strong policy against any postverdict inquiry into a juror's state of mind and conduct during deliberations. Only the strongest of evidence that a particular juror suffered from incompetence to understand the issues or deliberate at the time of service should justify inquiry into whether such incompetence did exist. Generally, a person is deemed incapable of consent to sexual relations when he/she is less than 17 years-old, is mentally defective, is mentally incapacitated, or is physically helpless. Mentally defective refers to that state where a person suffers from a mental condition that renders him/her incapable of appraising the nature of his/her conduct. This determination which bears upon the outcome of a number of sex offense cases must involve psychiatric examination of an alleged victim. Case reports are outlined to illustrate the psycholegal collaborations involved in the types of competency determinations discussed. Seventy-one footnotes are listed.