The concept of computer diagnosis in medicine is not new. As early as 1971, a computer program was demonstrated to be more accurate than a senior clinician at diagnosing acute abdominal pain before surgery. In psychiatry, however, the problems surrounding diagnosis and classification are more complex than in other branches of medicine, depending as they do on the clinical interview and some agreed classificatory system in the absence of external validating criteria. Reliability has been improved by the application of standardised interview techniques and by the use of operationalised diagnostic criteria but such tools are lengthy and their use requires specialist training. Consequently they tend to be reserved for research purposes rather than routine clinical use. The potential contribution of computer technology to the vexed question of psychiatric diagnosis is here evaluated.