Using Google, the world's most popular internet search engine, could help doctors to diagnose difficult cases, an Australian study suggests.

Doctors at the Princess Alexandra Hospital in Brisbane identified 26 difficult diagnostic cases published in the New England Journal of Medicine in 2005.

These included conditions such as Cushing's syndrome and Creutzfeldt-Jakob disease.

They selected three to five search terms from each case and did a Google search while blind to the correct diagnoses.

The doctors then selected and recorded the three diagnoses that were ranked most prominently and selected the one which seemed most relevant to the signs.

The results were then compared with the correct diagnoses as published in the journal.

Google searches found the correct diagnosis in 15 (58 per cent) of cases.

The doctors believe that Google is likely to be a useful aid for conditions with unique symptoms and signs that can easily be used as search terms.

However, they warned that the efficiency of the search and the usefulness of the retrieved information depend on the searchers’ knowledge base.

Lead researcher Dr Hangwi Tang said: "Doctors and patients are increasingly using the internet to search for health related information, and useful information on even the rarest medical syndromes can now be found and digested within a matter of minutes.

"Our study suggests that in difficult diagnostic cases, it is often useful to Google for a diagnosis."

The work is published on the British Medical Journal website.

Google is the most popular search engine on the web, giving users access to more than three billion medical articles.

The company's share of the global online search market is about 50 per cent, according to tracking firm Nielsen Media Research.

Yahoo is second with nearly 23 per cent share, followed by MSN (10.7 per cent) and AOL (6.6 per cent).