Mental health professionals who become involved in child sexual abuse potentially fulfill a number of roles that are not necessarily compatible: reporter of suspected abuse; investigator; evaluator; mediator; expert witness, whether at adjudication, disposition, or sentencing; victim therapist; or perpetrator therapist. The clinician who both investigates the allegation of abuse and treats either the child victim or the perpetrator confronts an intractable conflict in roles. This conflict can be avoided only by focusing mental health professionals' involvement in clinical evaluation and treatment. Separating these roles by ensuring that a clinician who investigates does not treat reduces but does not eliminate the conflict. Therefore, mental health professionals should not be involved in investigating child sexual abuse cases. In addition, mental health testimony about the victim should never be allowed during the adjudication stage, and mental health testimony about the defendant should be allowed only for defendants who put their character into question. The scientific knowledge base for such testimony is limited, and the testimony is likely to be more misleading and prejudicial than helpful. However, mental health professionals could appropriately help children and adults prepare for legal proceedings and facilitate mediation. 67 reference notes (Author abstract modified)