Over the past several years, numerous State appellate courts and legal commentators have addressed the admissibility of expert testimony offered by the prosecution regarding typical psychological behaviors of child sexual abuse victims and offenders. Defense attacks on a child's credibility are often based on such behaviors as the child's delay in reporting, retraction of his or her claim of abuse, initial minimization of the abuse, inconsistent accounts, or affection for the offender. As direct, substantive evidence of abuse, prosecutors have offered experts to testify about typical behaviors, profiles, syndromes, or common reactions of sexually abused children and also to express an opinion about a particular child. Problems with the admissibility of several forms of expert testimony are discussed in terms of legal requirements for expert testimony, prior juror knowledge of the issues, reliability of social science research on child sexual abuse, and prejudicial impact on jurors. The author concludes that expert testimony regarding common behaviors or reactions of sexually abused children or opinions that a child is a victim of abuse should probably be excluded, since such testimony fails to meet basic evidence requirements for admissibility. Further research is recommended to assess the impact of expert testimony on jurors and to explore legal and ethical issues associated with the use of expert testimony. A multidisciplinary symposium of professionals from psychology, social work, psychiatry, medicine, and law is also recommended to debate the admission of expert testimony in child sexual abuse cases. 63 references