Thousands of computer systems targeted at medical diagnosis (often described as expert systems) have been developed during the past 50 years. Most have had relatively little impact on day to day clinical practice; for example, because they are not easily accessible at the point of care; have a complex interface; can deal with only a narrow focus (one symptom or clinical problem); are not integrated with clinical information systems; depend on particular software or hardware platforms; or require labour intensive construction and are therefore expensive to maintain and extend.

In this week's BMJ a study by Tang and Ng assesses the effectiveness of a web search engine (Google) as a diagnostic aid.1 Using general purpose web search engines as a diagnostic aid is new, although using computers to aid diagnosis is not. …