Abstract Hardware and software used within the telecommunications industry must combine great complexity with high reliability. Production and maintenance of communications equipment requires many different kinds of human expertise. There is growing interest in the potential of expert systems to assist, or perhaps to replace, human experts. It is important to ensure that the expert systems are reliable and accurate; consequently, they must be evaluated. We review published experience with expert systems in the telecommunications industry and we propose some principles that we feel could usefully be adopted for their evaluation.