Comments that many ethical pitfalls may await psychologists who participate as expert witnesses in the legal process. This article describes the ethical problems and examines their origin in light of important differences in purpose between psychological practice and legal process. Special attention is given to problems of objectivity in the assessment process, ethical issues in the interpretation of data in the courtroom, and the client's psychological welfare. Suggestions for maintaining ethical practice in the role of expert witness are provided. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)